diff --git a/chrome/nsChromeRegistry.cpp b/chrome/nsChromeRegistry.cpp
index 31d1945e80fe..bfd1be490b84 100644
--- a/chrome/nsChromeRegistry.cpp
+++ b/chrome/nsChromeRegistry.cpp
@@ -39,6 +39,7 @@ nsChromeRegistry* nsChromeRegistry::gChromeRegistry;
 
 // DO NOT use namespace mozilla; it'll break due to a naming conflict between
 // mozilla::TextRange and a TextRange in OSX headers.
+using mozilla::ServoStyleSheet;
 using mozilla::StyleSheet;
 using mozilla::dom::IsChromeURI;
 using mozilla::dom::Location;
@@ -403,12 +404,12 @@ nsresult nsChromeRegistry::RefreshWindow(nsPIDOMWindowOuter* aWindow)
   nsCOMPtr<nsIPresShell> shell = document->GetShell();
   if (shell) {
     // Reload only the chrome URL agent style sheets.
-    nsTArray<RefPtr<StyleSheet>> agentSheets;
+    nsTArray<RefPtr<ServoStyleSheet>> agentSheets;
     rv = shell->GetAgentStyleSheets(agentSheets);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    nsTArray<RefPtr<StyleSheet>> newAgentSheets;
-    for (StyleSheet* sheet : agentSheets) {
+    nsTArray<RefPtr<ServoStyleSheet>> newAgentSheets;
+    for (ServoStyleSheet* sheet : agentSheets) {
       nsIURI* uri = sheet->GetSheetURI();
 
       if (IsChromeURI(uri)) {
@@ -417,7 +418,8 @@ nsresult nsChromeRegistry::RefreshWindow(nsPIDOMWindowOuter* aWindow)
         rv = document->LoadChromeSheetSync(uri, true, &newSheet);
         if (NS_FAILED(rv)) return rv;
         if (newSheet) {
-          rv = newAgentSheets.AppendElement(newSheet) ? NS_OK : NS_ERROR_FAILURE;
+          rv = newAgentSheets.AppendElement(newSheet->AsServo())
+            ? NS_OK : NS_ERROR_FAILURE;
           if (NS_FAILED(rv)) return rv;
         }
       }
diff --git a/dom/animation/KeyframeEffectReadOnly.cpp b/dom/animation/KeyframeEffectReadOnly.cpp
index ea5a48df9ab0..419339b8466b 100644
--- a/dom/animation/KeyframeEffectReadOnly.cpp
+++ b/dom/animation/KeyframeEffectReadOnly.cpp
@@ -408,10 +408,8 @@ KeyframeEffectReadOnly::EnsureBaseStyle(
     Element* animatingElement =
       EffectCompositor::GetElementToRestyle(mTarget->mElement,
                                             mTarget->mPseudoType);
-    aBaseComputedStyle =
-      aPresContext->StyleSet()->AsServo()->GetBaseContextForElement(
-          animatingElement,
-          aComputedStyle);
+    aBaseComputedStyle = aPresContext->StyleSet()->
+      GetBaseContextForElement(animatingElement, aComputedStyle);
   }
   RefPtr<RawServoAnimationValue> baseValue =
     Servo_ComputedValues_ExtractAnimationValue(aBaseComputedStyle,
@@ -1488,8 +1486,7 @@ KeyframeEffectReadOnly::CreateComputedStyleForAnimationValue(
              "CreateComputedStyleForAnimationValue needs to be called "
              "with a valid ComputedStyle");
 
-  ServoStyleSet* styleSet =
-    aBaseComputedStyle->PresContext()->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = aBaseComputedStyle->PresContext()->StyleSet();
   Element* elementForResolve =
     EffectCompositor::GetElementToRestyle(mTarget->mElement,
                                           mTarget->mPseudoType);
diff --git a/dom/animation/KeyframeUtils.cpp b/dom/animation/KeyframeUtils.cpp
index 8baedba2b495..bf77fe0193b6 100644
--- a/dom/animation/KeyframeUtils.cpp
+++ b/dom/animation/KeyframeUtils.cpp
@@ -930,8 +930,8 @@ GetComputedKeyframeValues(const nsTArray<Keyframe>& aKeyframes,
     return result;
   }
 
-  result = presContext->StyleSet()->AsServo()
-    ->GetComputedKeyframeValuesFor(aKeyframes, aElement, aComputedStyle);
+  result = presContext->StyleSet()->
+    GetComputedKeyframeValuesFor(aKeyframes, aElement, aComputedStyle);
   return result;
 }
 
diff --git a/dom/base/ResponsiveImageSelector.cpp b/dom/base/ResponsiveImageSelector.cpp
index 1f8fb0c70627..36d8dd97b6c2 100644
--- a/dom/base/ResponsiveImageSelector.cpp
+++ b/dom/base/ResponsiveImageSelector.cpp
@@ -440,9 +440,8 @@ ResponsiveImageSelector::ComputeFinalWidthForCurrentViewport(double *aWidth)
   if (!pctx) {
     return false;
   }
-  nscoord effectiveWidth =
-    presShell->StyleSet()->AsServo()->EvaluateSourceSizeList(
-      mServoSourceSizeList.get());
+  nscoord effectiveWidth = presShell->StyleSet()->
+    EvaluateSourceSizeList(mServoSourceSizeList.get());
 
   *aWidth = nsPresContext::AppUnitsToDoubleCSSPixels(std::max(effectiveWidth, 0));
   return true;
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 9ffea09eef07..7271aefbeb0c 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -246,8 +246,7 @@
 #include "mozilla/dom/FontFaceSet.h"
 #include "gfxPrefs.h"
 #include "nsISupportsPrimitives.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/StyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
 #include "mozilla/dom/SVGSVGElement.h"
@@ -2457,7 +2456,7 @@ nsIDocument::RemoveDocStyleSheetsFromStyleSets()
     if (sheet->IsApplicable()) {
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
-        shell->StyleSet()->RemoveDocStyleSheet(sheet);
+        shell->StyleSet()->RemoveDocStyleSheet(sheet->AsServo());
       }
     }
     // XXX Tell observers?
@@ -2476,7 +2475,7 @@ nsIDocument::RemoveStyleSheetsFromStyleSets(
     if (sheet->IsApplicable()) {
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
-        shell->StyleSet()->RemoveStyleSheet(aType, sheet);
+        shell->StyleSet()->RemoveStyleSheet(aType, sheet->AsServo());
       }
     }
     // XXX Tell observers?
@@ -2538,18 +2537,18 @@ nsIDocument::ResetStylesheetsToURI(nsIURI* aURI)
 }
 
 static void
-AppendSheetsToStyleSet(StyleSetHandle aStyleSet,
+AppendSheetsToStyleSet(ServoStyleSet* aStyleSet,
                        const nsTArray<RefPtr<StyleSheet>>& aSheets,
                        SheetType aType)
 {
   for (StyleSheet* sheet : Reversed(aSheets)) {
-    aStyleSet->AppendStyleSheet(aType, sheet);
+    aStyleSet->AppendStyleSheet(aType, sheet->AsServo());
   }
 }
 
 
 void
-nsIDocument::FillStyleSet(StyleSetHandle aStyleSet)
+nsIDocument::FillStyleSet(ServoStyleSet* aStyleSet)
 {
   NS_PRECONDITION(aStyleSet, "Must have a style set");
   NS_PRECONDITION(aStyleSet->SheetCount(SheetType::Doc) == 0,
@@ -2559,7 +2558,7 @@ nsIDocument::FillStyleSet(StyleSetHandle aStyleSet)
 
   for (StyleSheet* sheet : Reversed(mStyleSheets)) {
     if (sheet->IsApplicable()) {
-      aStyleSet->AddDocStyleSheet(sheet, this);
+      aStyleSet->AddDocStyleSheet(sheet->AsServo(), this);
     }
   }
 
@@ -2567,14 +2566,14 @@ nsIDocument::FillStyleSet(StyleSetHandle aStyleSet)
     nsTArray<RefPtr<StyleSheet>>& sheets =
       *sheetService->AuthorStyleSheets();
     for (StyleSheet* sheet : sheets) {
-      aStyleSet->AppendStyleSheet(SheetType::Doc, sheet);
+      aStyleSet->AppendStyleSheet(SheetType::Doc, sheet->AsServo());
     }
   }
 
   // Iterate backwards to maintain order
   for (StyleSheet* sheet : Reversed(mOnDemandBuiltInUASheets)) {
     if (sheet->IsApplicable()) {
-      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
   }
 
@@ -3878,19 +3877,19 @@ AssertNoStaleServoDataIn(const nsINode& aSubtreeRoot)
 already_AddRefed<nsIPresShell>
 nsIDocument::CreateShell(nsPresContext* aContext,
                          nsViewManager* aViewManager,
-                         StyleSetHandle aStyleSet)
+                         UniquePtr<ServoStyleSet> aStyleSet)
 {
   NS_ASSERTION(!mPresShell, "We have a presshell already!");
 
   NS_ENSURE_FALSE(GetBFCacheEntry(), nullptr);
 
-  FillStyleSet(aStyleSet);
+  FillStyleSet(aStyleSet.get());
   AssertNoStaleServoDataIn(static_cast<nsINode&>(*this));
 
   RefPtr<PresShell> shell = new PresShell;
   // Note: we don't hold a ref to the shell (it holds a ref to us)
   mPresShell = shell;
-  shell->Init(this, aContext, aViewManager, aStyleSet);
+  shell->Init(this, aContext, aViewManager, Move(aStyleSet));
 
   // Make sure to never paint if we belong to an invisible DocShell.
   nsCOMPtr<nsIDocShell> docShell(mDocumentContainer);
@@ -4311,7 +4310,7 @@ nsIDocument::AddOnDemandBuiltInUASheet(StyleSheet* aSheet)
       // do not override Firefox OS/Mobile's content.css sheet. Maybe we should
       // have an insertion point to match the order of
       // nsDocumentViewer::CreateStyleSet though?
-      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet);
+      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet->AsServo());
     }
   }
 
@@ -4323,7 +4322,7 @@ nsIDocument::AddStyleSheetToStyleSets(StyleSheet* aSheet)
 {
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
-    shell->StyleSet()->AddDocStyleSheet(aSheet, this);
+    shell->StyleSet()->AddDocStyleSheet(aSheet->AsServo(), this);
   }
 }
 
@@ -4390,7 +4389,7 @@ nsIDocument::RemoveStyleSheetFromStyleSets(StyleSheet* aSheet)
 {
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
-    shell->StyleSet()->RemoveDocStyleSheet(aSheet);
+    shell->StyleSet()->RemoveDocStyleSheet(aSheet->AsServo());
   }
 }
 
@@ -4611,7 +4610,7 @@ nsIDocument::AddAdditionalStyleSheet(additionalSheetType aType, StyleSheet* aShe
   nsCOMPtr<nsIPresShell> shell = GetShell();
   if (shell) {
     SheetType type = ConvertAdditionalSheetType(aType);
-    shell->StyleSet()->AppendStyleSheet(type, aSheet);
+    shell->StyleSet()->AppendStyleSheet(type, aSheet->AsServo());
   }
 
   // Passing false, so documet.styleSheets.length will not be affected by
@@ -4639,7 +4638,7 @@ nsIDocument::RemoveAdditionalStyleSheet(additionalSheetType aType, nsIURI* aShee
       nsCOMPtr<nsIPresShell> shell = GetShell();
       if (shell) {
         SheetType type = ConvertAdditionalSheetType(aType);
-        shell->StyleSet()->RemoveStyleSheet(type, sheetRef);
+        shell->StyleSet()->RemoveStyleSheet(type, sheetRef->AsServo());
       }
     }
 
diff --git a/dom/base/nsDocument.h b/dom/base/nsDocument.h
index 9ce5e631ea7c..5d0d6e3c5e7c 100644
--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -41,7 +41,6 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsContentList.h"
 #include "nsGkAtoms.h"
-#include "mozilla/StyleSetHandle.h"
 #include "PLDHashTable.h"
 #include "nsDOMAttributeMap.h"
 #include "imgIRequest.h"
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index eebf02f9c38c..e607ce1b4045 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -130,7 +130,7 @@ class ErrorResult;
 class EventStates;
 class EventListenerManager;
 class PendingAnimationTracker;
-class StyleSetHandle;
+class ServoStyleSet;
 template<typename> class OwningNonNull;
 struct URLExtraData;
 
@@ -1181,9 +1181,10 @@ class nsIDocument : public nsINode,
    * method is responsible for calling BeginObservingDocument() on the
    * presshell if the presshell should observe document mutations.
    */
-  already_AddRefed<nsIPresShell> CreateShell(nsPresContext* aContext,
-                                             nsViewManager* aViewManager,
-                                             mozilla::StyleSetHandle aStyleSet);
+  already_AddRefed<nsIPresShell> CreateShell(
+    nsPresContext* aContext,
+    nsViewManager* aViewManager,
+    mozilla::UniquePtr<mozilla::ServoStyleSet> aStyleSet);
   void DeleteShell();
 
   nsIPresShell* GetShell() const
@@ -3715,7 +3716,7 @@ class nsIDocument : public nsINode,
       const nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets,
       mozilla::SheetType aType);
   void ResetStylesheetsToURI(nsIURI* aURI);
-  void FillStyleSet(mozilla::StyleSetHandle aStyleSet);
+  void FillStyleSet(mozilla::ServoStyleSet* aStyleSet);
   void AddStyleSheetToStyleSets(mozilla::StyleSheet* aSheet);
   void RemoveStyleSheetFromStyleSets(mozilla::StyleSheet* aSheet);
   void NotifyStyleSheetAdded(mozilla::StyleSheet* aSheet, bool aDocumentSheet);
diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index e6faa976d9e3..c2127989d4d9 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -119,8 +119,7 @@
 #include "Units.h"
 #include "CanvasUtils.h"
 #include "mozilla/CycleCollectedJSRuntime.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/layers/CanvasClient.h"
 #include "mozilla/layers/WebRenderUserData.h"
 #include "mozilla/layers/WebRenderCanvasRenderer.h"
@@ -743,23 +742,12 @@ CanvasGradient::AddColorStop(float aOffset, const nsAString& aColorstr, ErrorRes
     return;
   }
 
-  nscolor color;
-  bool ok;
-
   nsIPresShell* shell = mContext ? mContext->GetPresShell() : nullptr;
-  ServoStyleSet* servoStyleSet = shell && shell->StyleSet()
-    ? shell->StyleSet()->GetAsServo()
-    : nullptr;
+  ServoStyleSet* styleSet = shell ? shell->StyleSet() : nullptr;
 
-  bool useServoParser =
-    true;
-
-  if (useServoParser) {
-    ok = ServoCSSParser::ComputeColor(servoStyleSet, NS_RGB(0, 0, 0), aColorstr,
-                                      &color);
-  } else {
-    MOZ_CRASH("old style system disabled");
-  }
+  nscolor color;
+  bool ok = ServoCSSParser::ComputeColor(styleSet, NS_RGB(0, 0, 0),
+                                         aColorstr, &color);
 
   if (!ok) {
     aRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);
@@ -1158,34 +1146,27 @@ CanvasRenderingContext2D::ParseColor(const nsAString& aString,
   nsIDocument* document = mCanvasElement ? mCanvasElement->OwnerDoc() : nullptr;
   css::Loader* loader = document ? document->CSSLoader() : nullptr;
 
-  bool useServoParser =
-    true;
+  nsIPresShell* presShell = GetPresShell();
+  ServoStyleSet* set = presShell ? presShell->StyleSet() : nullptr;
 
-  if (useServoParser) {
-    nsIPresShell* presShell = GetPresShell();
-    ServoStyleSet* set = presShell ? presShell->StyleSet()->AsServo() : nullptr;
-
-    // First, try computing the color without handling currentcolor.
-    bool wasCurrentColor = false;
-    if (!ServoCSSParser::ComputeColor(set, NS_RGB(0, 0, 0), aString, aColor,
-                                      &wasCurrentColor, loader)) {
-      return false;
-    }
+  // First, try computing the color without handling currentcolor.
+  bool wasCurrentColor = false;
+  if (!ServoCSSParser::ComputeColor(set, NS_RGB(0, 0, 0), aString, aColor,
+                                    &wasCurrentColor, loader)) {
+    return false;
+  }
 
-    if (wasCurrentColor && mCanvasElement) {
-      // Otherwise, get the value of the color property, flushing style
-      // if necessary.
-      RefPtr<ComputedStyle> canvasStyle =
-        nsComputedDOMStyle::GetComputedStyle(mCanvasElement, nullptr);
-      if (canvasStyle) {
-        *aColor = canvasStyle->StyleColor()->mColor;
-      }
-      // Beware that the presShell could be gone here.
+  if (wasCurrentColor && mCanvasElement) {
+    // Otherwise, get the value of the color property, flushing style
+    // if necessary.
+    RefPtr<ComputedStyle> canvasStyle =
+      nsComputedDOMStyle::GetComputedStyle(mCanvasElement, nullptr);
+    if (canvasStyle) {
+      *aColor = canvasStyle->StyleColor()->mColor;
     }
-    return true;
+    // Beware that the presShell could be gone here.
   }
-
-  MOZ_CRASH("old style system disabled");
+  return true;
 }
 
 nsresult
@@ -2704,7 +2685,7 @@ GetFontStyleForServo(Element* aElement, const nsAString& aFont,
     return nullptr;
   }
 
-  ServoStyleSet* styleSet = aPresShell->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
 
   RefPtr<ComputedStyle> parentStyle;
   // have to get a parent ComputedStyle for inherit-like relative
@@ -2723,7 +2704,7 @@ GetFontStyleForServo(Element* aElement, const nsAString& aFont,
                                     aPresShell->GetDocument());
     MOZ_ASSERT(declarations);
 
-    parentStyle = aPresShell->StyleSet()->AsServo()->
+    parentStyle = aPresShell->StyleSet()->
       ResolveForDeclarations(nullptr, declarations);
   }
 
@@ -2772,7 +2753,7 @@ ResolveFilterStyleForServo(const nsAString& aFilterString,
     return nullptr;
   }
 
-  ServoStyleSet* styleSet = aPresShell->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
   RefPtr<ComputedStyle> computedValues =
     styleSet->ResolveForDeclarations(aParentStyle, declarations);
 
diff --git a/dom/html/nsGenericHTMLElement.cpp b/dom/html/nsGenericHTMLElement.cpp
index dcd454e3d4a2..a46982a61118 100644
--- a/dom/html/nsGenericHTMLElement.cpp
+++ b/dom/html/nsGenericHTMLElement.cpp
@@ -99,8 +99,6 @@
 #include "mozilla/dom/HTMLBodyElement.h"
 #include "imgIContainer.h"
 #include "nsComputedDOMStyle.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "ReferrerPolicy.h"
 #include "mozilla/dom/HTMLLabelElement.h"
 #include "mozilla/dom/HTMLInputElement.h"
diff --git a/dom/html/nsHTMLDocument.cpp b/dom/html/nsHTMLDocument.cpp
index 8574906301f3..5d12f8f451d2 100644
--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -2257,7 +2257,7 @@ nsHTMLDocument::TearingDownEditor()
     if (!presShell)
       return;
 
-    nsTArray<RefPtr<StyleSheet>> agentSheets;
+    nsTArray<RefPtr<ServoStyleSheet>> agentSheets;
     presShell->GetAgentStyleSheets(agentSheets);
 
     auto cache = nsLayoutStylesheetCache::Singleton();
@@ -2402,13 +2402,14 @@ nsHTMLDocument::EditingStateChanged()
     // Before making this window editable, we need to modify UA style sheet
     // because new style may change whether focused element will be focusable
     // or not.
-    nsTArray<RefPtr<StyleSheet>> agentSheets;
+    nsTArray<RefPtr<ServoStyleSheet>> agentSheets;
     rv = presShell->GetAgentStyleSheets(agentSheets);
     NS_ENSURE_SUCCESS(rv, rv);
 
     auto cache = nsLayoutStylesheetCache::Singleton();
 
-    StyleSheet* contentEditableSheet = cache->ContentEditableSheet();
+    ServoStyleSheet* contentEditableSheet =
+      cache->ContentEditableSheet()->AsServo();
 
     if (!agentSheets.Contains(contentEditableSheet)) {
       agentSheets.AppendElement(contentEditableSheet);
@@ -2419,7 +2420,7 @@ nsHTMLDocument::EditingStateChanged()
     // specific states on the elements.
     if (designMode) {
       // designMode is being turned on (overrides contentEditable).
-      StyleSheet* designModeSheet = cache->DesignModeSheet();
+      ServoStyleSheet* designModeSheet = cache->DesignModeSheet()->AsServo();
       if (!agentSheets.Contains(designModeSheet)) {
         agentSheets.AppendElement(designModeSheet);
       }
@@ -2429,7 +2430,7 @@ nsHTMLDocument::EditingStateChanged()
     }
     else if (oldState == eDesignMode) {
       // designMode is being turned off (contentEditable is still on).
-      agentSheets.RemoveElement(cache->DesignModeSheet());
+      agentSheets.RemoveElement(cache->DesignModeSheet()->AsServo());
       updateState = true;
     }
 
diff --git a/dom/smil/nsSMILCSSValueType.cpp b/dom/smil/nsSMILCSSValueType.cpp
index 7cf7e46744b1..8c105379e301 100644
--- a/dom/smil/nsSMILCSSValueType.cpp
+++ b/dom/smil/nsSMILCSSValueType.cpp
@@ -19,7 +19,7 @@
 #include "mozilla/ServoBindings.h"
 #include "mozilla/StyleAnimationValue.h" // For AnimationValue
 #include "mozilla/ServoCSSParser.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/dom/BaseKeyframeTypesBinding.h" // For CompositeOperation
 #include "mozilla/dom/Element.h"
 #include "nsDebug.h"
@@ -518,10 +518,9 @@ ValueFromStringHelper(nsCSSPropertyID aPropID,
   }
 
   // Compute value
-  aPresContext->StyleSet()->AsServo()->GetAnimationValues(servoDeclarationBlock,
-                                                          aTargetElement,
-                                                          aComputedStyle,
-                                                          result);
+  aPresContext->StyleSet()->
+    GetAnimationValues(servoDeclarationBlock, aTargetElement,
+                       aComputedStyle, result);
 
   return result;
 }
diff --git a/dom/xbl/nsBindingManager.cpp b/dom/xbl/nsBindingManager.cpp
index 6fb71783f948..750a0c6c6b19 100644
--- a/dom/xbl/nsBindingManager.cpp
+++ b/dom/xbl/nsBindingManager.cpp
@@ -51,7 +51,6 @@
 #include "nsThreadUtils.h"
 #include "mozilla/dom/NodeListBinding.h"
 #include "mozilla/dom/ScriptSettings.h"
-#include "mozilla/ServoStyleSet.h"
 #include "mozilla/Unused.h"
 
 using namespace mozilla;
diff --git a/dom/xbl/nsXBLPrototypeResources.cpp b/dom/xbl/nsXBLPrototypeResources.cpp
index 75edbdc470ea..0d9ed74121ee 100644
--- a/dom/xbl/nsXBLPrototypeResources.cpp
+++ b/dom/xbl/nsXBLPrototypeResources.cpp
@@ -108,7 +108,7 @@ nsXBLPrototypeResources::FlushSkinSheets()
   // There may be no shell during unlink.
   if (auto* shell = doc->GetShell()) {
     MOZ_ASSERT(shell->GetPresContext());
-    ComputeServoStyles(*shell->StyleSet()->AsServo());
+    ComputeServoStyles(*shell->StyleSet());
   }
 
   return NS_OK;
diff --git a/dom/xbl/nsXBLResourceLoader.cpp b/dom/xbl/nsXBLResourceLoader.cpp
index 3a38ad2cc5e2..84949d6b7c88 100644
--- a/dom/xbl/nsXBLResourceLoader.cpp
+++ b/dom/xbl/nsXBLResourceLoader.cpp
@@ -180,7 +180,7 @@ nsXBLResourceLoader::StyleSheetLoaded(StyleSheet* aSheet,
   if (mPendingSheets == 0) {
     // All stylesheets are loaded.
     mResources->ComputeServoStyles(
-      *mBoundDocument->GetShell()->StyleSet()->AsServo());
+      *mBoundDocument->GetShell()->StyleSet());
 
     // XXX Check for mPendingScripts when scripts also come online.
     if (!mInLoadResourcesFunc)
diff --git a/dom/xbl/nsXBLService.cpp b/dom/xbl/nsXBLService.cpp
index cb8412bfaca4..0f65e6ec4102 100644
--- a/dom/xbl/nsXBLService.cpp
+++ b/dom/xbl/nsXBLService.cpp
@@ -402,7 +402,7 @@ EnsureSubtreeStyled(Element* aElement)
     return;
   }
 
-  ServoStyleSet* servoSet = presShell->StyleSet()->AsServo();
+  ServoStyleSet* servoSet = presShell->StyleSet();
   StyleChildrenIterator iter(aElement);
   for (nsIContent* child = iter.GetNextChild();
        child;
@@ -465,7 +465,7 @@ class MOZ_RAII AutoStyleElement
     if (*mResolveStyle) {
       mElement->ClearServoData();
 
-      ServoStyleSet* servoSet = presShell->StyleSet()->AsServo();
+      ServoStyleSet* servoSet = presShell->StyleSet();
       servoSet->StyleNewSubtree(mElement);
     }
   }
diff --git a/editor/libeditor/HTMLAnonymousNodeEditor.cpp b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
index 5e2127c4cf4f..7defe0303648 100644
--- a/editor/libeditor/HTMLAnonymousNodeEditor.cpp
+++ b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
@@ -208,12 +208,11 @@ HTMLEditor::CreateAnonymousElement(nsAtom* aTag,
 
   // Must style the new element, otherwise the PostRecreateFramesFor call
   // below will do nothing.
-  if (ServoStyleSet* styleSet = ps->StyleSet()->GetAsServo()) {
-    // Sometimes editor likes to append anonymous content to elements
-    // in display:none subtrees, so avoid styling in those cases.
-    if (ServoStyleSet::MayTraverseFrom(newContent)) {
-      styleSet->StyleNewSubtree(newContent);
-    }
+  ServoStyleSet* styleSet = ps->StyleSet();
+  // Sometimes editor likes to append anonymous content to elements
+  // in display:none subtrees, so avoid styling in those cases.
+  if (ServoStyleSet::MayTraverseFrom(newContent)) {
+    styleSet->StyleNewSubtree(newContent);
   }
 
   ElementDeletionObserver* observer =
diff --git a/gfx/layers/apz/util/ActiveElementManager.cpp b/gfx/layers/apz/util/ActiveElementManager.cpp
index 48cbd9786226..096235f1ec38 100644
--- a/gfx/layers/apz/util/ActiveElementManager.cpp
+++ b/gfx/layers/apz/util/ActiveElementManager.cpp
@@ -7,8 +7,6 @@
 #include "ActiveElementManager.h"
 #include "mozilla/EventStateManager.h"
 #include "mozilla/EventStates.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/Preferences.h"
 #include "base/message_loop.h"
 #include "base/task.h"
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index b294eed0612f..e5e85298ba82 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -181,8 +181,7 @@
 #include "nsLayoutStylesheetCache.h"
 #include "mozilla/layers/InputAPZContext.h"
 #include "mozilla/layers/FocusTarget.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/StyleSheet.h"
 #include "mozilla/StyleSheetInlines.h"
 #include "mozilla/dom/ImageTracker.h"
@@ -905,7 +904,7 @@ PresShell::~PresShell()
 
   MOZ_ASSERT(mAllocatedPointers.IsEmpty(), "Some pres arena objects were not freed");
 
-  mStyleSet->Delete();
+  mStyleSet = nullptr;
   delete mFrameConstructor;
 
   mCurrentEventContent = nullptr;
@@ -921,7 +920,7 @@ void
 PresShell::Init(nsIDocument* aDocument,
                 nsPresContext* aPresContext,
                 nsViewManager* aViewManager,
-                StyleSetHandle aStyleSet)
+                UniquePtr<ServoStyleSet> aStyleSet)
 {
   NS_PRECONDITION(aDocument, "null ptr");
   NS_PRECONDITION(aPresContext, "null ptr");
@@ -957,7 +956,7 @@ PresShell::Init(nsIDocument* aDocument,
   // Now we can initialize the style set. Make sure to set the member before
   // calling Init, since various subroutines need to find the style set off
   // the PresContext during initialization.
-  mStyleSet = aStyleSet;
+  mStyleSet = Move(aStyleSet);
   mStyleSet->Init(aPresContext);
 
   // Notify our prescontext that it now has a compatibility mode.  Note that
@@ -1513,7 +1512,7 @@ PresShell::UpdatePreferenceStyles()
 
   RemovePreferenceStyles();
 
-  mStyleSet->AppendStyleSheet(SheetType::User, newPrefSheet);
+  mStyleSet->AppendStyleSheet(SheetType::User, newPrefSheet->AsServo());
   mPrefStyleSheet = newPrefSheet;
 
   mStyleSet->EndUpdate();
@@ -1523,7 +1522,7 @@ void
 PresShell::RemovePreferenceStyles()
 {
   if (mPrefStyleSheet) {
-    mStyleSet->RemoveStyleSheet(SheetType::User, mPrefStyleSheet);
+    mStyleSet->RemoveStyleSheet(SheetType::User, mPrefStyleSheet->AsServo());
     mPrefStyleSheet = nullptr;
   }
 }
@@ -1546,13 +1545,13 @@ PresShell::AddUserSheet(StyleSheet* aSheet)
   // Iterate forwards when removing so the searches for RemoveStyleSheet are as
   // short as possible.
   for (StyleSheet* sheet : userSheets) {
-    mStyleSet->RemoveStyleSheet(SheetType::User, sheet);
+    mStyleSet->RemoveStyleSheet(SheetType::User, sheet->AsServo());
   }
 
   // Now iterate backwards, so that the order of userSheets will be the same as
   // the order of sheets from it in the style set.
   for (StyleSheet* sheet : Reversed(userSheets)) {
-    mStyleSet->PrependStyleSheet(SheetType::User, sheet);
+    mStyleSet->PrependStyleSheet(SheetType::User, sheet->AsServo());
   }
 
   mStyleSet->EndUpdate();
@@ -1564,7 +1563,7 @@ PresShell::AddAgentSheet(StyleSheet* aSheet)
 {
   // Make sure this does what nsDocumentViewer::CreateStyleSet does
   // wrt ordering.
-  mStyleSet->AppendStyleSheet(SheetType::Agent, aSheet);
+  mStyleSet->AppendStyleSheet(SheetType::Agent, aSheet->AsServo());
   RestyleForCSSRuleChanges();
 }
 
@@ -1576,9 +1575,10 @@ PresShell::AddAuthorSheet(StyleSheet* aSheet)
   StyleSheet* firstAuthorSheet =
     mDocument->GetFirstAdditionalAuthorSheet();
   if (firstAuthorSheet) {
-    mStyleSet->InsertStyleSheetBefore(SheetType::Doc, aSheet, firstAuthorSheet);
+    mStyleSet->InsertStyleSheetBefore(SheetType::Doc, aSheet->AsServo(),
+                                      firstAuthorSheet->AsServo());
   } else {
-    mStyleSet->AppendStyleSheet(SheetType::Doc, aSheet);
+    mStyleSet->AppendStyleSheet(SheetType::Doc, aSheet->AsServo());
   }
 
   RestyleForCSSRuleChanges();
@@ -1587,7 +1587,7 @@ PresShell::AddAuthorSheet(StyleSheet* aSheet)
 void
 PresShell::RemoveSheet(SheetType aType, StyleSheet* aSheet)
 {
-  mStyleSet->RemoveStyleSheet(aType, aSheet);
+  mStyleSet->RemoveStyleSheet(aType, aSheet->AsServo());
   RestyleForCSSRuleChanges();
 }
 
@@ -4366,7 +4366,7 @@ PresShell::DocumentStatesChanged(nsIDocument* aDocument, EventStates aStateMask)
   MOZ_ASSERT(!aStateMask.IsEmpty());
 
   if (mDidInitialize) {
-    mStyleSet->AsServo()->InvalidateStyleForDocumentStateChanges(aStateMask);
+    mStyleSet->InvalidateStyleForDocumentStateChanges(aStateMask);
   }
 
   if (aStateMask.HasState(NS_DOCUMENT_STATE_WINDOW_INACTIVE)) {
@@ -8395,7 +8395,7 @@ PresShell::IsVisible()
 }
 
 nsresult
-PresShell::GetAgentStyleSheets(nsTArray<RefPtr<StyleSheet>>& aSheets)
+PresShell::GetAgentStyleSheets(nsTArray<RefPtr<ServoStyleSheet>>& aSheets)
 {
   aSheets.Clear();
   int32_t sheetCount = mStyleSet->SheetCount(SheetType::Agent);
@@ -8405,7 +8405,7 @@ PresShell::GetAgentStyleSheets(nsTArray<RefPtr<StyleSheet>>& aSheets)
   }
 
   for (int32_t i = 0; i < sheetCount; ++i) {
-    StyleSheet* sheet = mStyleSet->StyleSheetAt(SheetType::Agent, i);
+    ServoStyleSheet* sheet = mStyleSet->StyleSheetAt(SheetType::Agent, i);
     aSheets.AppendElement(sheet);
   }
 
@@ -8413,7 +8413,7 @@ PresShell::GetAgentStyleSheets(nsTArray<RefPtr<StyleSheet>>& aSheets)
 }
 
 nsresult
-PresShell::SetAgentStyleSheets(const nsTArray<RefPtr<StyleSheet>>& aSheets)
+PresShell::SetAgentStyleSheets(const nsTArray<RefPtr<ServoStyleSheet>>& aSheets)
 {
   return mStyleSet->ReplaceSheets(SheetType::Agent, aSheets);
 }
@@ -8421,13 +8421,13 @@ PresShell::SetAgentStyleSheets(const nsTArray<RefPtr<StyleSheet>>& aSheets)
 nsresult
 PresShell::AddOverrideStyleSheet(StyleSheet* aSheet)
 {
-  return mStyleSet->PrependStyleSheet(SheetType::Override, aSheet);
+  return mStyleSet->PrependStyleSheet(SheetType::Override, aSheet->AsServo());
 }
 
 nsresult
 PresShell::RemoveOverrideStyleSheet(StyleSheet* aSheet)
 {
-  return mStyleSet->RemoveStyleSheet(SheetType::Override, aSheet);
+  return mStyleSet->RemoveStyleSheet(SheetType::Override, aSheet->AsServo());
 }
 
 static void
@@ -9495,11 +9495,11 @@ FindTopFrame(nsIFrame* aRoot)
 #ifdef DEBUG
 
 static void
-CopySheetsIntoClone(StyleSetHandle aSet, StyleSetHandle aClone)
+CopySheetsIntoClone(ServoStyleSet* aSet, ServoStyleSet* aClone)
 {
   int32_t i, n = aSet->SheetCount(SheetType::Override);
   for (i = 0; i < n; i++) {
-    StyleSheet* ss = aSet->StyleSheetAt(SheetType::Override, i);
+    ServoStyleSheet* ss = aSet->StyleSheetAt(SheetType::Override, i);
     if (ss)
       aClone->AppendStyleSheet(SheetType::Override, ss);
   }
@@ -9516,25 +9516,25 @@ CopySheetsIntoClone(StyleSetHandle aSet, StyleSetHandle aClone)
 
   n = aSet->SheetCount(SheetType::User);
   for (i = 0; i < n; i++) {
-    StyleSheet* ss = aSet->StyleSheetAt(SheetType::User, i);
+    ServoStyleSheet* ss = aSet->StyleSheetAt(SheetType::User, i);
     if (ss)
       aClone->AppendStyleSheet(SheetType::User, ss);
   }
 
   n = aSet->SheetCount(SheetType::Agent);
   for (i = 0; i < n; i++) {
-    StyleSheet* ss = aSet->StyleSheetAt(SheetType::Agent, i);
+    ServoStyleSheet* ss = aSet->StyleSheetAt(SheetType::Agent, i);
     if (ss)
       aClone->AppendStyleSheet(SheetType::Agent, ss);
   }
 }
 
 
-ServoStyleSet*
+UniquePtr<ServoStyleSet>
 PresShell::CloneStyleSet(ServoStyleSet* aSet)
 {
-  ServoStyleSet* clone = new ServoStyleSet();
-  CopySheetsIntoClone(aSet, clone);
+  auto clone = MakeUnique<ServoStyleSet>();
+  CopySheetsIntoClone(aSet, clone.get());
   return clone;
 }
 
@@ -9588,12 +9588,10 @@ PresShell::VerifyIncrementalReflow()
 
   // Create a new presentation shell to view the document. Use the
   // exact same style information that this document has.
-  nsAutoPtr<ServoStyleSet> newServoSet(CloneStyleSet(mStyleSet->AsServo()));
-  StyleSetHandle newSet(newServoSet);
+  UniquePtr<ServoStyleSet> newSet = CloneStyleSet(StyleSet());
 
-  nsCOMPtr<nsIPresShell> sh = mDocument->CreateShell(cx, vm, newSet);
+  nsCOMPtr<nsIPresShell> sh = mDocument->CreateShell(cx, vm, Move(newSet));
   NS_ENSURE_TRUE(sh, false);
-  newServoSet.forget();
   // Note that after we create the shell, we must make sure to destroy it
   sh->SetVerifyReflowEnable(false); // turn off verify reflow while we're reflowing the test frame tree
   vm->SetPresShell(sh);
@@ -10321,7 +10319,7 @@ PresShell::AddSizeOfIncludingThis(nsWindowSizes& aSizes) const
     mApproximatelyVisibleFrames.ShallowSizeOfExcludingThis(mallocSizeOf) +
     mFramesToDirty.ShallowSizeOfExcludingThis(mallocSizeOf);
 
-  StyleSet()->AsServo()->AddSizeOfIncludingThis(aSizes);
+  StyleSet()->AddSizeOfIncludingThis(aSizes);
 
   aSizes.mLayoutTextRunsSize += SizeOfTextRuns(mallocSizeOf);
 
diff --git a/layout/base/PresShell.h b/layout/base/PresShell.h
index 63dc9f9c4d7b..f9a97735730e 100644
--- a/layout/base/PresShell.h
+++ b/layout/base/PresShell.h
@@ -14,7 +14,7 @@
 #include "mozilla/EventForwards.h"
 #include "mozilla/layers/FocusTarget.h"
 #include "mozilla/MemoryReporting.h"
-#include "mozilla/StyleSetHandle.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/UniquePtr.h"
 #include "nsAutoPtr.h"
 #include "nsContentUtils.h" // For AddScriptBlocker().
@@ -45,6 +45,7 @@ class nsAutoCauseReflowNotifier;
 class AutoPointerEventTargetUpdater;
 
 namespace mozilla {
+class ServoStyleSheet;
 
 namespace dom {
 class Element;
@@ -81,7 +82,8 @@ class PresShell final : public nsIPresShell,
   static bool AccessibleCaretEnabled(nsIDocShell* aDocShell);
 
   void Init(nsIDocument* aDocument, nsPresContext* aPresContext,
-            nsViewManager* aViewManager, StyleSetHandle aStyleSet);
+            nsViewManager* aViewManager,
+            UniquePtr<ServoStyleSet> aStyleSet);
   void Destroy() override;
 
   void UpdatePreferenceStyles() override;
@@ -158,9 +160,9 @@ class PresShell final : public nsIPresShell,
   void UnsuppressPainting() override;
 
   nsresult GetAgentStyleSheets(
-      nsTArray<RefPtr<StyleSheet>>& aSheets) override;
+      nsTArray<RefPtr<ServoStyleSheet>>& aSheets) override;
   nsresult SetAgentStyleSheets(
-      const nsTArray<RefPtr<StyleSheet>>& aSheets) override;
+      const nsTArray<RefPtr<ServoStyleSheet>>& aSheets) override;
 
   nsresult AddOverrideStyleSheet(StyleSheet* aSheet) override;
   nsresult RemoveOverrideStyleSheet(StyleSheet* aSheet) override;
@@ -505,7 +507,7 @@ class PresShell final : public nsIPresShell,
   bool mCaretEnabled;
 
 #ifdef DEBUG
-  ServoStyleSet* CloneStyleSet(ServoStyleSet* aSet);
+  UniquePtr<ServoStyleSet> CloneStyleSet(ServoStyleSet* aSet);
   bool VerifyIncrementalReflow();
   bool mInVerifyReflow;
   void ShowEventTargetDebug();
diff --git a/layout/base/RestyleManager.cpp b/layout/base/RestyleManager.cpp
index 963e9c63fc56..e18383b8c10f 100644
--- a/layout/base/RestyleManager.cpp
+++ b/layout/base/RestyleManager.cpp
@@ -9,8 +9,6 @@
 
 #include "Layers.h"
 #include "LayerAnimationInfo.h" // For LayerAnimationInfo::sRecords
-#include "mozilla/StyleSetHandleInlines.h"
-#include "mozilla/ServoStyleSetInlines.h"
 #include "nsAnimationManager.h"
 #include "nsCSSFrameConstructor.h"
 #include "nsCSSRendering.h"
diff --git a/layout/base/ServoRestyleManager.cpp b/layout/base/ServoRestyleManager.cpp
index 3d33a7686b84..4bd1910da41f 100644
--- a/layout/base/ServoRestyleManager.cpp
+++ b/layout/base/ServoRestyleManager.cpp
@@ -12,7 +12,7 @@
 #include "mozilla/ComputedStyleInlines.h"
 #include "mozilla/DocumentStyleRootIterator.h"
 #include "mozilla/ServoBindings.h"
-#include "mozilla/ServoStyleSet.h"
+#include "mozilla/ServoStyleSetInlines.h"
 #include "mozilla/Unused.h"
 #include "mozilla/ViewportFrame.h"
 #include "mozilla/dom/ChildIterator.h"
@@ -1547,7 +1547,7 @@ ServoRestyleManager::ReparentComputedStyle(nsIFrame* aFrame)
 
 void
 ServoRestyleManager::DoReparentComputedStyle(nsIFrame* aFrame,
-                                            ServoStyleSet& aStyleSet)
+                                             ServoStyleSet& aStyleSet)
 {
   if (aFrame->IsBackdropFrame()) {
     // Style context of backdrop frame has no parent style, and thus we do not
diff --git a/layout/base/ServoRestyleManager.h b/layout/base/ServoRestyleManager.h
index c93988fd4327..c769da0049df 100644
--- a/layout/base/ServoRestyleManager.h
+++ b/layout/base/ServoRestyleManager.h
@@ -19,6 +19,7 @@ namespace mozilla {
 namespace dom {
 class Element;
 } // namespace dom
+class ServoStyleSet;
 } // namespace mozilla
 class nsAttrValue;
 class nsAtom;
@@ -303,10 +304,7 @@ class ServoRestyleManager : public RestyleManager
                                    ServoRestyleState& aRestyleState,
                                    ServoPostTraversalFlags aFlags);
 
-  inline ServoStyleSet* StyleSet() const
-  {
-    return PresContext()->StyleSet()->AsServo();
-  }
+  inline ServoStyleSet* StyleSet() const { return PresContext()->StyleSet(); }
 
   const SnapshotTable& Snapshots() const { return mSnapshots; }
   void ClearSnapshots();
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index 3a4f00dcc473..b7939dba2f9e 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -40,8 +40,6 @@
 #include "nsHTMLParts.h"
 #include "nsIPresShell.h"
 #include "nsUnicharUtils.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsViewManager.h"
 #include "nsStyleConsts.h"
 #ifdef MOZ_XUL
@@ -1831,7 +1829,7 @@ nsCSSFrameConstructor::CreateGeneratedContentItem(nsFrameConstructorState& aStat
              aPseudoElement == CSSPseudoElementType::after,
              "unexpected aPseudoElement");
 
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
 
   // Probe for the existence of the pseudo-element
   RefPtr<ComputedStyle> pseudoComputedStyle;
@@ -1889,9 +1887,8 @@ nsCSSFrameConstructor::CreateGeneratedContentItem(nsFrameConstructorState& aStat
     // If animations are involved, we avoid the SetExplicitStyle optimization
     // above. We need to grab style with animations from the pseudo element
     // and replace old one.
-    mPresShell->StyleSet()->AsServo()->StyleNewSubtree(container);
-    pseudoComputedStyle =
-      styleSet->AsServo()->ResolveServoStyle(container);
+    mPresShell->StyleSet()->StyleNewSubtree(container);
+    pseudoComputedStyle = styleSet->ResolveServoStyle(container);
   }
 
   uint32_t contentCount = pseudoComputedStyle->StyleContent()->ContentCount();
@@ -1904,7 +1901,7 @@ nsCSSFrameConstructor::CreateGeneratedContentItem(nsFrameConstructorState& aStat
       if (content->IsElement()) {
         // If we created any children elements, Servo needs to traverse them, but
         // the root is already set up.
-        mPresShell->StyleSet()->AsServo()->StyleNewSubtree(content->AsElement());
+        mPresShell->StyleSet()->StyleNewSubtree(content->AsElement());
       }
     }
   }
@@ -2433,18 +2430,17 @@ nsCSSFrameConstructor::ConstructDocElementFrame(Element*                 aDocEle
     state.mPresShell->CaptureHistoryState(getter_AddRefs(mTempFrameTreeState));
 
   // --------- CREATE AREA OR BOX FRAME -------
-  if (ServoStyleSet* set = mPresShell->StyleSet()->GetAsServo()) {
-    // Ensure the document element is styled at this point.
-    if (!aDocElement->HasServoData()) {
-      // NOTE(emilio): If the root has a non-null binding, we'll stop at the
-      // document element and won't process any children, loading the bindings
-      // (or failing to do so) will take care of the rest.
-      set->StyleNewSubtree(aDocElement);
-    }
+  ServoStyleSet* set = mPresShell->StyleSet();
+  // Ensure the document element is styled at this point.
+  if (!aDocElement->HasServoData()) {
+    // NOTE(emilio): If the root has a non-null binding, we'll stop at the
+    // document element and won't process any children, loading the bindings
+    // (or failing to do so) will take care of the rest.
+    set->StyleNewSubtree(aDocElement);
   }
 
   RefPtr<ComputedStyle> computedStyle =
-    mPresShell->StyleSet()->AsServo()->ResolveServoStyle(aDocElement);
+    mPresShell->StyleSet()->ResolveServoStyle(aDocElement);
 
   const nsStyleDisplay* display = computedStyle->StyleDisplay();
 
@@ -2476,8 +2472,7 @@ nsCSSFrameConstructor::ConstructDocElementFrame(Element*                 aDocEle
     }
 
     if (resolveStyle) {
-      computedStyle =
-        mPresShell->StyleSet()->AsServo()->ResolveServoStyle(aDocElement);
+      computedStyle = mPresShell->StyleSet()->ResolveServoStyle(aDocElement);
       display = computedStyle->StyleDisplay();
     }
   }
@@ -2685,7 +2680,7 @@ nsCSSFrameConstructor::ConstructRootFrame()
 {
   AUTO_LAYOUT_PHASE_ENTRY_POINT(mPresShell->GetPresContext(), FrameC);
 
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
 
   // --------- BUILD VIEWPORT -----------
   RefPtr<ComputedStyle> viewportPseudoStyle =
@@ -2852,7 +2847,7 @@ nsCSSFrameConstructor::SetUpDocElementContainingBlock(nsIContent* aDocElement)
   // Start off with the viewport as parent; we'll adjust it as needed.
   nsContainerFrame* parentFrame = viewportFrame;
 
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
   // If paginated, make sure we don't put scrollbars in
   if (!isScrollable) {
     rootPseudoStyle =
@@ -2956,7 +2951,7 @@ nsCSSFrameConstructor::ConstructPageFrame(nsIPresShell*  aPresShell,
                                           nsContainerFrame*& aCanvasFrame)
 {
   ComputedStyle* parentComputedStyle = aParentFrame->Style();
-  StyleSetHandle styleSet = aPresShell->StyleSet();
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
 
   RefPtr<ComputedStyle> pagePseudoStyle;
   pagePseudoStyle =
@@ -4240,12 +4235,11 @@ nsCSSFrameConstructor::GetAnonymousContent(nsIContent* aParent,
     }
   }
 
-  if (ServoStyleSet* styleSet = mPresShell->StyleSet()->GetAsServo()) {
-    // Eagerly compute styles for the anonymous content tree.
-    for (auto& info : aContent) {
-      if (info.mContent->IsElement()) {
-        styleSet->StyleNewSubtree(info.mContent->AsElement());
-      }
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
+  // Eagerly compute styles for the anonymous content tree.
+  for (auto& info : aContent) {
+    if (info.mContent->IsElement()) {
+      styleSet->StyleNewSubtree(info.mContent->AsElement());
     }
   }
 
@@ -4598,7 +4592,7 @@ nsCSSFrameConstructor::BeginBuildingScrollFrame(nsFrameConstructorState& aState,
   gfxScrollFrame->AddStateBits(NS_FRAME_OWNS_ANON_BOXES);
 
   // we used the style that was passed in. So resolve another one.
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
   RefPtr<ComputedStyle> scrolledChildStyle =
     styleSet->ResolveInheritingAnonymousBoxStyle(aScrolledPseudo, contentStyle);
 
@@ -5009,7 +5003,7 @@ nsCSSFrameConstructor::InitAndRestoreFrame(const nsFrameConstructorState& aState
 already_AddRefed<ComputedStyle>
 nsCSSFrameConstructor::ResolveComputedStyle(nsIContent* aContent)
 {
-  ServoStyleSet* styleSet = mPresShell->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
 
   if (aContent->IsElement()) {
     return styleSet->ResolveServoStyle(aContent->AsElement());
@@ -5055,7 +5049,7 @@ nsCSSFrameConstructor::FlushAccumulatedBlock(nsFrameConstructorState& aState,
   ComputedStyle* parentContext =
     nsFrame::CorrectStyleParentFrame(aParentFrame,
                                      anonPseudo)->Style();
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
   RefPtr<ComputedStyle> blockContext;
   blockContext = styleSet->
     ResolveInheritingAnonymousBoxStyle(anonPseudo, parentContext);
@@ -5696,7 +5690,7 @@ nsCSSFrameConstructor::AddFrameConstructionItemsInternal(nsFrameConstructorState
 
       if (resolveStyle) {
         computedStyle =
-          mPresShell->StyleSet()->AsServo()->ResolveServoStyle(aContent->AsElement());
+          mPresShell->StyleSet()->ResolveServoStyle(aContent->AsElement());
       }
 
       display = computedStyle->StyleDisplay();
@@ -7077,7 +7071,7 @@ void
 nsCSSFrameConstructor::StyleNewChildRange(nsIContent* aStartChild,
                                           nsIContent* aEndChild)
 {
-  ServoStyleSet* styleSet = mPresShell->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
 
   for (nsIContent* child = aStartChild; child != aEndChild;
        child = child->GetNextSibling()) {
@@ -10753,7 +10747,7 @@ nsCSSFrameConstructor::CreateFloatingLetterFrame(
   // Make sure we get a proper style for it (the one passed in is for the letter
   // frame and will have the float property set on it; the text frame shouldn't
   // have that set).
-  StyleSetHandle styleSet = mPresShell->StyleSet();
+  ServoStyleSet* styleSet = mPresShell->StyleSet();
   RefPtr<ComputedStyle> textSC = styleSet->
     ResolveStyleForText(aTextContent, aComputedStyle);
   aTextFrame->SetComputedStyleWithoutNotification(textSC);
@@ -10834,7 +10828,7 @@ nsCSSFrameConstructor::CreateLetterFrame(nsContainerFrame* aBlockFrame,
                                          nsCSSPseudoElements::firstLetter);
 
       sc =
-        mPresShell->StyleSet()->AsServo()->ReparentComputedStyle(
+        mPresShell->StyleSet()->ReparentComputedStyle(
           sc,
           parentComputedStyle,
           parentIgnoringFirstLine->Style(),
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index c67888fd664e..ce54c516659f 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -22,8 +22,6 @@
 #include "nsIDocument.h"
 #include "nsPresContext.h"
 #include "nsIPresShell.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsIFrame.h"
 #include "nsIWritablePropertyBag2.h"
 #include "nsSubDocumentFrame.h"
@@ -685,17 +683,17 @@ nsDocumentViewer::InitPresentationStuff(bool aDoInitialReflow)
                "Someone should have destroyed the presshell!");
 
   // Create the style set...
-  StyleSetHandle styleSet = CreateStyleSet(mDocument);
+  UniquePtr<ServoStyleSet> styleSet = CreateStyleSet(mDocument);
 
   // Now make the shell for the document
-  mPresShell = mDocument->CreateShell(mPresContext, mViewManager, styleSet);
+  mPresShell = mDocument->CreateShell(mPresContext, mViewManager,
+                                      mozilla::Move(styleSet));
   if (!mPresShell) {
-    styleSet->Delete();
     return NS_ERROR_FAILURE;
   }
 
   // We're done creating the style set
-  styleSet->EndUpdate();
+  mPresShell->StyleSet()->EndUpdate();
 
   if (aDoInitialReflow) {
     // Since Initialize() will create frames for *all* items
@@ -2309,7 +2307,7 @@ nsDocumentViewer::RequestWindowClose(bool* aCanClose)
   return NS_OK;
 }
 
-StyleSetHandle
+UniquePtr<ServoStyleSet>
 nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
 {
   // Make sure this does the same thing as PresShell::AddSheet wrt ordering.
@@ -2317,7 +2315,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
   // this should eventually get expanded to allow for creating
   // different sets for different media
 
-  StyleSetHandle styleSet = new ServoStyleSet();
+  UniquePtr<ServoStyleSet> styleSet = MakeUnique<ServoStyleSet>();
 
   styleSet->BeginUpdate();
 
@@ -2347,8 +2345,9 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     sheet = cache->UserContentSheet();
   }
 
-  if (sheet)
-    styleSet->AppendStyleSheet(SheetType::User, sheet);
+  if (sheet) {
+    styleSet->AppendStyleSheet(SheetType::User, sheet->AsServo());
+  }
 
   // Append chrome sheets (scrollbars + forms).
   bool shouldOverride = false;
@@ -2384,7 +2383,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
           cssLoader->LoadSheetSync(uri, &chromeSheet);
           if (!chromeSheet) continue;
 
-          styleSet->PrependStyleSheet(SheetType::Agent, chromeSheet);
+          styleSet->PrependStyleSheet(SheetType::Agent, chromeSheet->AsServo());
           shouldOverride = true;
         }
         free(str);
@@ -2395,7 +2394,7 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
   if (!shouldOverride) {
     sheet = cache->ScrollbarsSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
   }
 
@@ -2411,26 +2410,26 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
 
     sheet = cache->NumberControlSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
 
     sheet = cache->FormsSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
 
     if (aDocument->LoadsFullXULStyleSheetUpFront()) {
       // This is the only place components.css gets loaded, unlike xul.css
       sheet = cache->XULComponentsSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
       }
 
       // nsXULElement::BindToTree loads xul.css on-demand if we don't load it
       // up-front here.
       sheet = cache->XULSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
       }
     }
 
@@ -2438,25 +2437,25 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     if (sheet) {
       // Load the minimal XUL rules for scrollbars and a few other XUL things
       // that non-XUL (typically HTML) documents commonly use.
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
 
     sheet = cache->CounterStylesSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
 
     if (nsLayoutUtils::ShouldUseNoScriptSheet(aDocument)) {
       sheet = cache->NoScriptSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
       }
     }
 
     if (nsLayoutUtils::ShouldUseNoFramesSheet(aDocument)) {
       sheet = cache->NoFramesSheet();
       if (sheet) {
-        styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+        styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
       }
     }
 
@@ -2465,26 +2464,26 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
 
     sheet = cache->HTMLSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
 
     styleSet->PrependStyleSheet(SheetType::Agent,
-                                cache->UASheet());
+                                cache->UASheet()->AsServo());
   } else {
     // SVG documents may have scrollbars and need the scrollbar styling.
     sheet = cache->MinimalXULSheet();
     if (sheet) {
-      styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+      styleSet->PrependStyleSheet(SheetType::Agent, sheet->AsServo());
     }
   }
 
   nsStyleSheetService* sheetService = nsStyleSheetService::GetInstance();
   if (sheetService) {
     for (StyleSheet* sheet : *sheetService->AgentStyleSheets()) {
-      styleSet->AppendStyleSheet(SheetType::Agent, sheet);
+      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsServo());
     }
     for (StyleSheet* sheet : Reversed(*sheetService->UserStyleSheets())) {
-      styleSet->PrependStyleSheet(SheetType::User, sheet);
+      styleSet->PrependStyleSheet(SheetType::User, sheet->AsServo());
     }
   }
 
diff --git a/layout/base/nsIDocumentViewerPrint.h b/layout/base/nsIDocumentViewerPrint.h
index 45207a1617c2..50ff526a9495 100644
--- a/layout/base/nsIDocumentViewerPrint.h
+++ b/layout/base/nsIDocumentViewerPrint.h
@@ -7,10 +7,11 @@
 #define nsIDocumentViewerPrint_h___
 
 #include "nsISupports.h"
+#include "mozilla/UniquePtr.h"
 
 class nsIDocument;
 namespace mozilla {
-class StyleSetHandle;
+class ServoStyleSet;
 } // namespace mozilla
 class nsIPresShell;
 class nsPresContext;
@@ -39,7 +40,8 @@ class nsIDocumentViewerPrint : public nsISupports
   // The style set returned by CreateStyleSet is in the middle of an
   // update batch so that the caller can add sheets to it if needed.
   // Callers should call EndUpdate() on it when ready to use.
-  virtual mozilla::StyleSetHandle CreateStyleSet(nsIDocument* aDocument) = 0;
+  virtual mozilla::UniquePtr<mozilla::ServoStyleSet>
+    CreateStyleSet(nsIDocument* aDocument) = 0;
 
   /**
    * This is used by nsPagePrintTimer to make nsDocumentViewer::Destroy()
@@ -78,7 +80,8 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsIDocumentViewerPrint,
   bool GetIsPrinting() override; \
   void SetIsPrintPreview(bool aIsPrintPreview) override; \
   bool GetIsPrintPreview() override; \
-  mozilla::StyleSetHandle CreateStyleSet(nsIDocument* aDocument) override; \
+  mozilla::UniquePtr<mozilla::ServoStyleSet> \
+    CreateStyleSet(nsIDocument* aDocument) override; \
   void IncrementDestroyBlockedCount() override; \
   void DecrementDestroyBlockedCount() override; \
   void OnDonePrinting() override; \
diff --git a/layout/base/nsIPresShell.h b/layout/base/nsIPresShell.h
index e28fe78271ea..d3b2a11d0797 100644
--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -13,9 +13,10 @@
 #include "mozilla/EventForwards.h"
 #include "mozilla/FlushType.h"
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/StaticPtr.h"
-#include "mozilla/StyleSetHandle.h"
 #include "mozilla/StyleSheet.h"
+#include "mozilla/UniquePtr.h"
 #include "mozilla/WeakPtr.h"
 #include "GeckoProfiler.h"
 #include "gfxPoint.h"
@@ -56,7 +57,7 @@ class nsCanvasFrame;
 class nsCaret;
 namespace mozilla {
 class AccessibleCaretEventHub;
-class CSSStyleSheet;
+class ServoStyleSheet;
 } // namespace mozilla
 class nsFrameSelection;
 class nsFrameManager;
@@ -278,7 +279,7 @@ class nsIPresShell : public nsStubDocumentObserver
   }
 #endif
 
-  mozilla::StyleSetHandle StyleSet() const { return mStyleSet; }
+  mozilla::ServoStyleSet* StyleSet() const { return mStyleSet.get(); }
 
   nsCSSFrameConstructor* FrameConstructor() const { return mFrameConstructor; }
 
@@ -993,13 +994,13 @@ class nsIPresShell : public nsStubDocumentObserver
    * Get the set of agent style sheets for this presentation
    */
   virtual nsresult GetAgentStyleSheets(
-      nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets) = 0;
+      nsTArray<RefPtr<mozilla::ServoStyleSheet>>& aSheets) = 0;
 
   /**
    * Replace the set of agent style sheets
    */
   virtual nsresult SetAgentStyleSheets(
-      const nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets) = 0;
+      const nsTArray<RefPtr<mozilla::ServoStyleSheet>>& aSheets) = 0;
 
   /**
    * Add an override style sheet for this presentation
@@ -1694,7 +1695,7 @@ class nsIPresShell : public nsStubDocumentObserver
   // we must share ownership.
   nsCOMPtr<nsIDocument>     mDocument;
   RefPtr<nsPresContext>   mPresContext;
-  mozilla::StyleSetHandle   mStyleSet;      // [OWNS]
+  mozilla::UniquePtr<mozilla::ServoStyleSet> mStyleSet;
   nsCSSFrameConstructor*    mFrameConstructor; // [OWNS]
   nsViewManager*           mViewManager;   // [WEAK] docViewer owns it so I don't have to
   nsPresArena               mFrameArena;
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 314d716e6ecf..7cb920c3f5ca 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -116,8 +116,7 @@
 #include "mozilla/Telemetry.h"
 #include "mozilla/EventDispatcher.h"
 #include "mozilla/StyleAnimationValue.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/WheelHandlingHelper.h" // for WheelHandlingUtils
 #include "RegionBuilder.h"
 #include "SVGViewportElement.h"
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index dc46555c1674..31743a9e8278 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -23,8 +23,7 @@
 #include "nsDocShell.h"
 #include "nsIContentViewer.h"
 #include "nsPIDOMWindow.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsIContent.h"
 #include "nsIFrame.h"
 #include "nsIDocument.h"
@@ -121,22 +120,11 @@ class ContainerLayerPresContext : public LayerUserData {
 nscolor
 nsPresContext::MakeColorPref(const nsString& aColor)
 {
-  bool ok;
-  nscolor result;
-
-  ServoStyleSet* servoStyleSet = mShell && mShell->StyleSet()
-    ? mShell->StyleSet()->GetAsServo()
-    : nullptr;
-
-  bool useServoParser =
-    true;
+  ServoStyleSet* styleSet = mShell ? mShell->StyleSet() : nullptr;
 
-  if (useServoParser) {
-    ok = ServoCSSParser::ComputeColor(servoStyleSet, NS_RGB(0, 0, 0), aColor,
-                                      &result);
-  } else {
-    MOZ_CRASH("old style system disabled");
-  }
+  nscolor result;
+  bool ok = ServoCSSParser::
+    ComputeColor(styleSet, NS_RGB(0, 0, 0), aColor, &result);
 
   if (!ok) {
     // Any better choices?
@@ -1202,8 +1190,8 @@ nsPresContext::CompatibilityModeChanged()
     return;
   }
 
-  StyleSetHandle styleSet = mShell->StyleSet();
-  styleSet->AsServo()->CompatibilityModeChanged();
+  ServoStyleSet* styleSet = mShell->StyleSet();
+  styleSet->CompatibilityModeChanged();
 
   if (doc->IsSVGDocument()) {
     // SVG documents never load quirk.css.
@@ -1221,11 +1209,11 @@ nsPresContext::CompatibilityModeChanged()
   if (needsQuirkSheet) {
     // quirk.css needs to come after html.css; we just keep it at the end.
     DebugOnly<nsresult> rv =
-      styleSet->AppendStyleSheet(SheetType::Agent, sheet);
+      styleSet->AppendStyleSheet(SheetType::Agent, sheet->AsServo());
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to insert quirk.css");
   } else {
     DebugOnly<nsresult> rv =
-      styleSet->RemoveStyleSheet(SheetType::Agent, sheet);
+      styleSet->RemoveStyleSheet(SheetType::Agent, sheet->AsServo());
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to remove quirk.css");
   }
 
@@ -1470,7 +1458,7 @@ GetPropagatedScrollbarStylesForViewport(nsPresContext* aPresContext,
   }
 
   // Check the style on the document root element
-  StyleSetHandle styleSet = aPresContext->StyleSet();
+  ServoStyleSet* styleSet = aPresContext->StyleSet();
   RefPtr<ComputedStyle> rootStyle =
     styleSet->ResolveStyleFor(docElement, nullptr, LazyComputeBehavior::Allow);
   if (CheckOverflow(rootStyle->StyleDisplay(), aStyles)) {
@@ -3022,7 +3010,7 @@ nsPresContext::FlushFontFeatureValues()
   }
 
   if (mFontFeatureValuesDirty) {
-    StyleSetHandle styleSet = mShell->StyleSet();
+    ServoStyleSet* styleSet = mShell->StyleSet();
     mFontFeatureValuesLookup = styleSet->BuildFontFeatureValueSet();
     mFontFeatureValuesDirty = false;
   }
diff --git a/layout/base/nsPresContext.h b/layout/base/nsPresContext.h
index 6ea3bb8e5cb4..2a51de0cba02 100644
--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -223,7 +223,8 @@ class nsPresContext : public nsISupports,
       return mDocument;
   }
 
-  mozilla::StyleSetHandle StyleSet() const { return GetPresShell()->StyleSet(); }
+  mozilla::ServoStyleSet* StyleSet() const
+    { return GetPresShell()->StyleSet(); }
 
   bool HasPendingMediaQueryUpdates() const
   {
diff --git a/layout/forms/nsButtonFrameRenderer.cpp b/layout/forms/nsButtonFrameRenderer.cpp
index 38f0bd3ed7ec..07e0c93d7c96 100644
--- a/layout/forms/nsButtonFrameRenderer.cpp
+++ b/layout/forms/nsButtonFrameRenderer.cpp
@@ -9,8 +9,7 @@
 #include "nsGkAtoms.h"
 #include "nsCSSPseudoElements.h"
 #include "nsNameSpaceManager.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/Unused.h"
 #include "nsDisplayList.h"
 #include "nsITheme.h"
@@ -559,7 +558,7 @@ nsButtonFrameRenderer::ReResolveStyles(nsPresContext* aPresContext)
 {
   // get all the styles
   ComputedStyle* context = mFrame->Style();
-  StyleSetHandle styleSet = aPresContext->StyleSet();
+  ServoStyleSet* styleSet = aPresContext->StyleSet();
 
   // get styles assigned to -moz-inner-focus (ie dotted border on Windows)
   mInnerFocusStyle =
diff --git a/layout/forms/nsColorControlFrame.cpp b/layout/forms/nsColorControlFrame.cpp
index fbd254e17535..0d553d872f40 100644
--- a/layout/forms/nsColorControlFrame.cpp
+++ b/layout/forms/nsColorControlFrame.cpp
@@ -13,8 +13,6 @@
 #include "nsGkAtoms.h"
 #include "nsIDOMNode.h"
 #include "nsIFormControl.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/dom/HTMLInputElement.h"
 #include "nsIDocument.h"
 
diff --git a/layout/forms/nsComboboxControlFrame.cpp b/layout/forms/nsComboboxControlFrame.cpp
index 43d7c919afa0..d72b781e8d68 100644
--- a/layout/forms/nsComboboxControlFrame.cpp
+++ b/layout/forms/nsComboboxControlFrame.cpp
@@ -33,8 +33,7 @@
 #include "nsIDocument.h"
 #include "nsIScrollableFrame.h"
 #include "nsListControlFrame.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsNodeInfoManager.h"
 #include "nsContentCreatorFunctions.h"
 #include "nsLayoutUtils.h"
@@ -1390,7 +1389,7 @@ nsComboboxControlFrame::CreateFrameForDisplayNode()
 
   // Get PresShell
   nsIPresShell *shell = PresShell();
-  StyleSetHandle styleSet = shell->StyleSet();
+  ServoStyleSet* styleSet = shell->StyleSet();
 
   // create the ComputedStyle for the anonymous block frame and text frame
   RefPtr<ComputedStyle> computedStyle;
diff --git a/layout/forms/nsGfxButtonControlFrame.cpp b/layout/forms/nsGfxButtonControlFrame.cpp
index cf6a26996293..4d524b5a03ae 100644
--- a/layout/forms/nsGfxButtonControlFrame.cpp
+++ b/layout/forms/nsGfxButtonControlFrame.cpp
@@ -7,8 +7,6 @@
 #include "nsGfxButtonControlFrame.h"
 #include "nsIFormControl.h"
 #include "nsGkAtoms.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/dom/HTMLInputElement.h"
 #include "nsContentUtils.h"
 #include "nsTextNode.h"
diff --git a/layout/forms/nsMeterFrame.cpp b/layout/forms/nsMeterFrame.cpp
index b11c671c09eb..9565cc3cf722 100644
--- a/layout/forms/nsMeterFrame.cpp
+++ b/layout/forms/nsMeterFrame.cpp
@@ -20,8 +20,6 @@
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/HTMLMeterElement.h"
 #include "nsCSSPseudoElements.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsThemeConstants.h"
 #include <algorithm>
 
diff --git a/layout/forms/nsNumberControlFrame.cpp b/layout/forms/nsNumberControlFrame.cpp
index 69669659fecb..675672f76baf 100644
--- a/layout/forms/nsNumberControlFrame.cpp
+++ b/layout/forms/nsNumberControlFrame.cpp
@@ -21,8 +21,6 @@
 #include "nsContentUtils.h"
 #include "nsContentCreatorFunctions.h"
 #include "nsCSSPseudoElements.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsThreadUtils.h"
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/dom/MutationEventBinding.h"
diff --git a/layout/forms/nsProgressFrame.cpp b/layout/forms/nsProgressFrame.cpp
index 0d60d479a1a2..b35606e71aaa 100644
--- a/layout/forms/nsProgressFrame.cpp
+++ b/layout/forms/nsProgressFrame.cpp
@@ -20,8 +20,6 @@
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/HTMLProgressElement.h"
 #include "nsCSSPseudoElements.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsThemeConstants.h"
 #include <algorithm>
 
diff --git a/layout/forms/nsRangeFrame.cpp b/layout/forms/nsRangeFrame.cpp
index dadc021b78d9..e5c759ee6d8b 100644
--- a/layout/forms/nsRangeFrame.cpp
+++ b/layout/forms/nsRangeFrame.cpp
@@ -24,8 +24,7 @@
 #include "nsPresContext.h"
 #include "nsNodeInfoManager.h"
 #include "mozilla/dom/Element.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsThemeConstants.h"
 
 #ifdef ACCESSIBILITY
@@ -79,7 +78,7 @@ nsRangeFrame::Init(nsIContent*       aContent,
   }
   aContent->AddEventListener(NS_LITERAL_STRING("touchstart"), mDummyTouchListener, false);
 
-  StyleSetHandle styleSet = PresContext()->StyleSet();
+  ServoStyleSet* styleSet = PresContext()->StyleSet();
 
   mOuterFocusStyle =
     styleSet->ProbePseudoElementStyle(aContent->AsElement(),
diff --git a/layout/forms/nsTextControlFrame.cpp b/layout/forms/nsTextControlFrame.cpp
index 14d4f0897735..c130a21f8410 100644
--- a/layout/forms/nsTextControlFrame.cpp
+++ b/layout/forms/nsTextControlFrame.cpp
@@ -40,8 +40,6 @@
 #include "mozilla/TextEditRules.h"
 #include "nsContentUtils.h"
 #include "nsTextNode.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/dom/HTMLInputElement.h"
 #include "mozilla/dom/HTMLTextAreaElement.h"
 #include "mozilla/dom/ScriptSettings.h"
diff --git a/layout/generic/nsBlockFrame.cpp b/layout/generic/nsBlockFrame.cpp
index 65df14a8a553..299463123840 100644
--- a/layout/generic/nsBlockFrame.cpp
+++ b/layout/generic/nsBlockFrame.cpp
@@ -56,8 +56,6 @@
 #include "mozilla/RestyleManagerInlines.h"
 #include "mozilla/ServoRestyleManager.h"
 #include "mozilla/ServoStyleSet.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/Telemetry.h"
 
 #include "nsBidiPresUtils.h"
@@ -7553,7 +7551,7 @@ nsBlockFrame::UpdatePseudoElementStyles(ServoRestyleState& aRestyleState)
 
 already_AddRefed<ComputedStyle>
 nsBlockFrame::ResolveBulletStyle(CSSPseudoElementType aType,
-                                 StyleSetHandle aStyleSet)
+                                 ServoStyleSet* aStyleSet)
 {
   ComputedStyle* parentStyle =
     CorrectStyleParentFrame(this,
diff --git a/layout/generic/nsBlockFrame.h b/layout/generic/nsBlockFrame.h
index 512f599ad587..2b498f01815e 100644
--- a/layout/generic/nsBlockFrame.h
+++ b/layout/generic/nsBlockFrame.h
@@ -45,7 +45,7 @@ class nsBulletFrame;
 namespace mozilla {
 class BlockReflowInput;
 class ServoRestyleState;
-class StyleSetHandle;
+class ServoStyleSet;
 } // namespace mozilla
 
 /**
@@ -943,7 +943,7 @@ class nsBlockFrame : public nsContainerFrame
   // optimization, because all callsites have it.
   already_AddRefed<ComputedStyle> ResolveBulletStyle(
     mozilla::CSSPseudoElementType aType,
-    mozilla::StyleSetHandle aStyleSet);
+    mozilla::ServoStyleSet* aStyleSet);
 
 #ifdef DEBUG
   void VerifyLines(bool aFinalCheckOK);
diff --git a/layout/generic/nsFirstLetterFrame.cpp b/layout/generic/nsFirstLetterFrame.cpp
index ac0f18fdabcf..238d10aa0447 100644
--- a/layout/generic/nsFirstLetterFrame.cpp
+++ b/layout/generic/nsFirstLetterFrame.cpp
@@ -12,8 +12,7 @@
 #include "nsIContent.h"
 #include "nsLineLayout.h"
 #include "nsGkAtoms.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsFrameManager.h"
 #include "mozilla/RestyleManager.h"
 #include "mozilla/RestyleManagerInlines.h"
diff --git a/layout/generic/nsFrameSetFrame.cpp b/layout/generic/nsFrameSetFrame.cpp
index b0d110008298..cb05690325c8 100644
--- a/layout/generic/nsFrameSetFrame.cpp
+++ b/layout/generic/nsFrameSetFrame.cpp
@@ -29,8 +29,7 @@
 #include "nsHTMLParts.h"
 #include "nsNameSpaceManager.h"
 #include "nsCSSAnonBoxes.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/dom/Element.h"
 #include "nsDisplayList.h"
 #include "nsNodeUtils.h"
@@ -803,7 +802,7 @@ nsHTMLFramesetFrame::Reflow(nsPresContext*           aPresContext,
   MOZ_ASSERT(aStatus.IsEmpty(), "Caller should pass a fresh reflow status!");
 
   nsIPresShell *shell = aPresContext->PresShell();
-  StyleSetHandle styleSet = shell->StyleSet();
+  ServoStyleSet* styleSet = shell->StyleSet();
 
   GetParent()->AddStateBits(NS_FRAME_CONTAINS_RELATIVE_BSIZE);
 
diff --git a/layout/generic/nsImageFrame.cpp b/layout/generic/nsImageFrame.cpp
index 3059478c96f3..c29a3ad0f150 100644
--- a/layout/generic/nsImageFrame.cpp
+++ b/layout/generic/nsImageFrame.cpp
@@ -71,8 +71,7 @@
 #include "gfxRect.h"
 #include "ImageLayers.h"
 #include "ImageContainer.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsBlockFrame.h"
 #include "nsStyleStructInlines.h"
 
diff --git a/layout/generic/nsInlineFrame.cpp b/layout/generic/nsInlineFrame.cpp
index 075e3e54776f..5eafc7d83ad4 100644
--- a/layout/generic/nsInlineFrame.cpp
+++ b/layout/generic/nsInlineFrame.cpp
@@ -22,8 +22,6 @@
 #include "SVGTextFrame.h"
 #include "nsStyleChangeList.h"
 #include "mozilla/ComputedStyle.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/ServoStyleSet.h"
 
 #ifdef DEBUG
diff --git a/layout/generic/nsTextFrame.cpp b/layout/generic/nsTextFrame.cpp
index a38849090758..7ad4f56de707 100644
--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -66,8 +66,7 @@
 #include "nsLineBreaker.h"
 #include "nsIFrameInlines.h"
 #include "mozilla/intl/WordBreaker.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/layers/LayersMessages.h"
 #include "mozilla/layers/WebRenderLayerManager.h"
 #include "mozilla/layers/WebRenderBridgeChild.h"
diff --git a/layout/inspector/InspectorUtils.cpp b/layout/inspector/InspectorUtils.cpp
index c8d74d9b2f0e..fad9628326cc 100644
--- a/layout/inspector/InspectorUtils.cpp
+++ b/layout/inspector/InspectorUtils.cpp
@@ -39,7 +39,7 @@
 #include "nsCSSProps.h"
 #include "nsCSSValue.h"
 #include "nsColor.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsStyleUtil.h"
 #include "nsQueryObject.h"
 #include "mozilla/ServoBindings.h"
@@ -67,7 +67,7 @@ InspectorUtils::GetAllStyleSheets(GlobalObject& aGlobalObject,
   nsIPresShell* presShell = aDocument.GetShell();
 
   if (presShell) {
-    StyleSetHandle styleSet = presShell->StyleSet();
+    ServoStyleSet* styleSet = presShell->StyleSet();
     SheetType sheetType = SheetType::Agent;
     for (int32_t i = 0; i < styleSet->SheetCount(sheetType); i++) {
       aResult.AppendElement(styleSet->StyleSheetAt(sheetType, i));
@@ -187,7 +187,7 @@ InspectorUtils::GetCSSStyleRules(GlobalObject& aGlobalObject,
 
   AutoTArray<ServoStyleRuleMap*, 1> maps;
   {
-    ServoStyleSet* styleSet = shell->StyleSet()->AsServo();
+    ServoStyleSet* styleSet = shell->StyleSet();
     ServoStyleRuleMap* map = styleSet->StyleRuleMap();
     maps.AppendElement(map);
   }
diff --git a/layout/mathml/nsMathMLFrame.cpp b/layout/mathml/nsMathMLFrame.cpp
index dca08ac74cb7..6a6abf8e5da1 100644
--- a/layout/mathml/nsMathMLFrame.cpp
+++ b/layout/mathml/nsMathMLFrame.cpp
@@ -17,8 +17,7 @@
 #include "gfxMathTable.h"
 
 // used to map attributes into CSS rules
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "nsDisplayList.h"
 
 using namespace mozilla;
diff --git a/layout/printing/nsPrintJob.cpp b/layout/printing/nsPrintJob.cpp
index 6102329db6f3..2149335ff643 100644
--- a/layout/printing/nsPrintJob.cpp
+++ b/layout/printing/nsPrintJob.cpp
@@ -119,8 +119,7 @@ static const char kPrintingPromptService[] = "@mozilla.org/embedcomp/printingpro
 #include "nsIChannel.h"
 #include "xpcpublic.h"
 #include "nsVariant.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -2345,19 +2344,20 @@ nsPrintJob::ReflowPrintObject(const UniquePtr<nsPrintObject>& aPO)
   rv = aPO->mViewManager->Init(printData->mPrintDC);
   NS_ENSURE_SUCCESS(rv,rv);
 
-  StyleSetHandle styleSet = mDocViewerPrint->CreateStyleSet(aPO->mDocument);
+  UniquePtr<ServoStyleSet> styleSet =
+    mDocViewerPrint->CreateStyleSet(aPO->mDocument);
 
   if (aPO->mDocument->IsSVGDocument()) {
     // The SVG document only loads minimal-xul.css, so it doesn't apply other
     // styles. We should add ua.css for applying style which related to print.
     auto cache = nsLayoutStylesheetCache::Singleton();
-    styleSet->PrependStyleSheet(SheetType::Agent, cache->UASheet());
+    styleSet->PrependStyleSheet(SheetType::Agent, cache->UASheet()->AsServo());
   }
 
   aPO->mPresShell = aPO->mDocument->CreateShell(aPO->mPresContext,
-                                                aPO->mViewManager, styleSet);
+                                                aPO->mViewManager,
+                                                Move(styleSet));
   if (!aPO->mPresShell) {
-    styleSet->Delete();
     return NS_ERROR_FAILURE;
   }
 
@@ -2369,7 +2369,7 @@ nsPrintJob::ReflowPrintObject(const UniquePtr<nsPrintObject>& aPO)
     DeleteUnselectedNodes(aPO->mDocument->GetOriginalDocument(), aPO->mDocument);
   }
 
-  styleSet->EndUpdate();
+  aPO->mPresShell->StyleSet()->EndUpdate();
 
   // The pres shell now owns the style set object.
 
diff --git a/layout/style/ComputedStyle.cpp b/layout/style/ComputedStyle.cpp
index 83057105a109..b2a2be5783f4 100644
--- a/layout/style/ComputedStyle.cpp
+++ b/layout/style/ComputedStyle.cpp
@@ -30,8 +30,6 @@
 #include "mozilla/ArenaObjectID.h"
 #include "mozilla/ComputedStyleInlines.h"
 #include "mozilla/Preferences.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 
 #include "mozilla/ReflowInput.h"
 #include "nsLayoutUtils.h"
diff --git a/layout/style/ComputedStyle.h b/layout/style/ComputedStyle.h
index 40842040e205..ab253e32a641 100644
--- a/layout/style/ComputedStyle.h
+++ b/layout/style/ComputedStyle.h
@@ -14,7 +14,6 @@
 #include "mozilla/ArenaObjectID.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/RestyleLogging.h"
-#include "mozilla/ServoStyleSet.h"
 #include "mozilla/ServoTypes.h"
 #include "mozilla/ServoUtils.h"
 #include "mozilla/StyleComplexColor.h"
diff --git a/layout/style/CounterStyleManager.cpp b/layout/style/CounterStyleManager.cpp
index 28ca7d56bf39..c8dba3cccbde 100644
--- a/layout/style/CounterStyleManager.cpp
+++ b/layout/style/CounterStyleManager.cpp
@@ -17,8 +17,7 @@
 #include "nsTArray.h"
 #include "nsTHashtable.h"
 #include "nsUnicodeProperties.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 
 namespace mozilla {
 
@@ -2035,7 +2034,7 @@ CounterStyleManager::BuildCounterStyle(nsAtom* aName)
 
   // Names are compared case-sensitively here. Predefined names should
   // have been lowercased by the parser.
-  StyleSetHandle styleSet = mPresContext->StyleSet();
+  ServoStyleSet* styleSet = mPresContext->StyleSet();
   nsCSSCounterStyleRule* rule = styleSet->CounterStyleRuleForName(aName);
   if (rule) {
     MOZ_ASSERT(rule->Name() == aName);
@@ -2086,7 +2085,7 @@ CounterStyleManager::NotifyRuleChanged()
     CounterStyle* style = iter.Data();
     bool toBeUpdated = false;
     bool toBeRemoved = false;
-    StyleSetHandle styleSet = mPresContext->StyleSet();
+    ServoStyleSet* styleSet = mPresContext->StyleSet();
     nsCSSCounterStyleRule* newRule = styleSet->CounterStyleRuleForName(iter.Key());
     if (!newRule) {
       if (style->IsCustomStyle()) {
diff --git a/layout/style/ServoMediaList.cpp b/layout/style/ServoMediaList.cpp
index b49a63c710c1..f433da8781d6 100644
--- a/layout/style/ServoMediaList.cpp
+++ b/layout/style/ServoMediaList.cpp
@@ -94,7 +94,7 @@ bool
 ServoMediaList::Matches(nsPresContext* aPresContext) const
 {
   const RawServoStyleSet* rawSet =
-    aPresContext->StyleSet()->AsServo()->RawSet();
+    aPresContext->StyleSet()->RawSet();
   MOZ_ASSERT(rawSet, "The RawServoStyleSet should be valid!");
   return Servo_MediaList_Matches(mRawList, rawSet);
 }
diff --git a/layout/style/ServoStyleSheet.cpp b/layout/style/ServoStyleSheet.cpp
index 9845ef85108e..278203f78507 100644
--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -11,7 +11,6 @@
 #include "mozilla/ServoCSSRuleList.h"
 #include "mozilla/ServoImportRule.h"
 #include "mozilla/ServoMediaList.h"
-#include "mozilla/ServoStyleSet.h"
 #include "mozilla/css/GroupRule.h"
 #include "mozilla/dom/CSSRuleList.h"
 #include "mozilla/dom/MediaList.h"
diff --git a/layout/style/StyleAnimationValue.cpp b/layout/style/StyleAnimationValue.cpp
index e1a39061a0b7..b26d363e2aac 100644
--- a/layout/style/StyleAnimationValue.cpp
+++ b/layout/style/StyleAnimationValue.cpp
@@ -11,8 +11,7 @@
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/ServoBindings.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/Tuple.h"
 #include "mozilla/UniquePtr.h"
 #include "nsAutoPtr.h"
@@ -241,10 +240,8 @@ AnimationValue::FromString(nsCSSPropertyID aProperty,
     return result;
   }
 
-  result.mServo =
-    shell->StyleSet()->AsServo()->ComputeAnimationValue(aElement,
-                                                        declarations,
-                                                        computedStyle);
+  result.mServo = shell->StyleSet()->
+    ComputeAnimationValue(aElement, declarations, computedStyle);
   return result;
 }
 
diff --git a/layout/style/StyleSetHandle.h b/layout/style/StyleSetHandle.h
deleted file mode 100644
index 2d7eb196c9e5..000000000000
--- a/layout/style/StyleSetHandle.h
+++ /dev/null
@@ -1,209 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef mozilla_StyleSetHandle_h
-#define mozilla_StyleSetHandle_h
-
-#include "mozilla/AtomArray.h"
-#include "mozilla/EventStates.h"
-#include "mozilla/MediaFeatureChange.h"
-#include "mozilla/RefPtr.h"
-#include "mozilla/ServoTypes.h"
-#include "mozilla/SheetType.h"
-#include "mozilla/StyleSheet.h"
-#include "nsChangeHint.h"
-#include "nsCSSPseudoElements.h"
-#include "nsTArray.h"
-
-class nsBindingManager;
-class nsCSSCounterStyleRule;
-struct nsFontFaceRuleContainer;
-class nsAtom;
-class nsICSSAnonBoxPseudo;
-class nsIContent;
-class nsIDocument;
-class nsStyleSet;
-class nsPresContext;
-class gfxFontFeatureValueSet;
-
-namespace mozilla {
-
-class ComputedStyle;
-class CSSStyleSheet;
-class ServoStyleSet;
-namespace dom {
-class Element;
-class ShadowRoot;
-} // namespace dom
-namespace css {
-class Rule;
-} // namespace css
-
-/**
- * Smart pointer class that can hold a pointer to either an nsStyleSet
- * or a ServoStyleSet.
- */
-class StyleSetHandle
-{
-public:
-  // We define this Ptr class with a StyleSet API that forwards on to the
-  // wrapped pointer, rather than putting these methods on StyleSetHandle
-  // itself, so that we can have StyleSetHandle behave like a smart pointer and
-  // be dereferenced with operator->.
-  class Ptr
-  {
-  public:
-    friend class ::mozilla::StyleSetHandle;
-
-    ServoStyleSet* AsServo()
-    {
-      return reinterpret_cast<ServoStyleSet*>(mValue);
-    }
-
-    ServoStyleSet* GetAsServo() { return AsServo(); }
-
-
-    const ServoStyleSet* AsServo() const
-    {
-      return const_cast<Ptr*>(this)->AsServo();
-    }
-
-    const ServoStyleSet* GetAsServo() const { return AsServo(); }
-
-    // These inline methods are defined in StyleSetHandleInlines.h.
-    inline void Delete();
-
-    // Style set interface.  These inline methods are defined in
-    // StyleSetHandleInlines.h and just forward to the underlying
-    // nsStyleSet or ServoStyleSet.  See corresponding comments in
-    // nsStyleSet.h for descriptions of these methods.
-
-    inline void Init(nsPresContext* aPresContext);
-    inline void BeginShutdown();
-    inline void Shutdown();
-    inline bool GetAuthorStyleDisabled() const;
-    inline void SetAuthorStyleDisabled(bool aStyleDisabled);
-    inline void BeginUpdate();
-    inline nsresult EndUpdate();
-    inline already_AddRefed<ComputedStyle>
-    ResolveStyleFor(dom::Element* aElement,
-                    ComputedStyle* aParentContext,
-                    LazyComputeBehavior aMayCompute);
-    inline already_AddRefed<ComputedStyle>
-    ResolveStyleFor(dom::Element* aElement, LazyComputeBehavior aMayCompute);
-
-    // TODO(emilio): This might be nicer (albeit a bit slower) if we just grab
-    // the style from the parent in ServoStyleSet.
-    //
-    // It may be faster if we account not having to pass it around in
-    // nsCSSFrameConstructor though.
-    inline already_AddRefed<ComputedStyle>
-    ResolveStyleForText(nsIContent* aTextNode, ComputedStyle* aParentContext);
-
-    inline already_AddRefed<ComputedStyle>
-    ResolveStyleForFirstLetterContinuation(ComputedStyle* aParentContext);
-    inline already_AddRefed<ComputedStyle>
-    ResolveStyleForPlaceholder();
-    inline already_AddRefed<ComputedStyle>
-    ResolvePseudoElementStyle(dom::Element* aParentElement,
-                              mozilla::CSSPseudoElementType aType,
-                              ComputedStyle* aParentContext,
-                              dom::Element* aPseudoElement);
-    inline already_AddRefed<ComputedStyle>
-    ResolveInheritingAnonymousBoxStyle(nsAtom* aPseudoTag,
-                                       ComputedStyle* aParentContext);
-    inline already_AddRefed<ComputedStyle>
-    ResolveNonInheritingAnonymousBoxStyle(nsAtom* aPseudoTag);
-#ifdef MOZ_XUL
-    inline already_AddRefed<ComputedStyle>
-    ResolveXULTreePseudoStyle(dom::Element* aParentElement,
-                              nsICSSAnonBoxPseudo* aPseudoTag,
-                              ComputedStyle* aParentContext,
-                              const AtomArray& aInputWord);
-#endif
-    inline nsresult AppendStyleSheet(SheetType aType, StyleSheet* aSheet);
-    inline nsresult PrependStyleSheet(SheetType aType, StyleSheet* aSheet);
-    inline nsresult RemoveStyleSheet(SheetType aType, StyleSheet* aSheet);
-    inline nsresult ReplaceSheets(SheetType aType,
-                           const nsTArray<RefPtr<StyleSheet>>& aNewSheets);
-    inline nsresult InsertStyleSheetBefore(SheetType aType,
-                                    StyleSheet* aNewSheet,
-                                    StyleSheet* aReferenceSheet);
-    inline int32_t SheetCount(SheetType aType) const;
-    inline StyleSheet* StyleSheetAt(SheetType aType, int32_t aIndex) const;
-    inline void AppendAllXBLStyleSheets(nsTArray<StyleSheet*>& aArray) const;
-    inline nsresult RemoveDocStyleSheet(StyleSheet* aSheet);
-    inline nsresult AddDocStyleSheet(StyleSheet* aSheet, nsIDocument* aDocument);
-
-    inline void RuleRemoved(StyleSheet&, css::Rule&);
-    inline void RuleAdded(StyleSheet&, css::Rule&);
-    inline void RuleChanged(StyleSheet&, css::Rule*);
-
-    inline void RecordShadowStyleChange(mozilla::dom::ShadowRoot& aShadowRoot);
-    inline bool StyleSheetsHaveChanged() const;
-    inline void InvalidateStyleForCSSRuleChanges();
-    inline nsRestyleHint MediumFeaturesChanged(mozilla::MediaFeatureChangeReason);
-    inline already_AddRefed<ComputedStyle>
-    ProbePseudoElementStyle(dom::Element* aParentElement,
-                            mozilla::CSSPseudoElementType aType,
-                            ComputedStyle* aParentContext);
-    inline already_AddRefed<ComputedStyle>
-    ProbePseudoElementStyle(dom::Element* aParentElement,
-                            mozilla::CSSPseudoElementType aType);
-
-    inline bool AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray);
-    inline nsCSSCounterStyleRule* CounterStyleRuleForName(nsAtom* aName);
-    inline already_AddRefed<gfxFontFeatureValueSet> BuildFontFeatureValueSet();
-
-    inline bool EnsureUniqueInnerOnCSSSheets();
-    inline void SetNeedsRestyleAfterEnsureUniqueInner();
-
-  private:
-    // Stores a pointer to an nsStyleSet or a ServoStyleSet.  The least
-    // significant bit is 0 for the former, 1 for the latter.  This is
-    // valid as the least significant bit will never be used for a pointer
-    // value on platforms we care about.
-    uintptr_t mValue;
-  };
-
-  StyleSetHandle() { mPtr.mValue = 0; }
-  StyleSetHandle(const StyleSetHandle& aOth) { mPtr.mValue = aOth.mPtr.mValue; }
-  MOZ_IMPLICIT StyleSetHandle(nsStyleSet* aSet) { *this = aSet; }
-  MOZ_IMPLICIT StyleSetHandle(ServoStyleSet* aSet) { *this = aSet; }
-
-  StyleSetHandle& operator=(nsStyleSet* aStyleSet)
-  {
-    mPtr.mValue = reinterpret_cast<uintptr_t>(aStyleSet);
-    return *this;
-  }
-
-  StyleSetHandle& operator=(ServoStyleSet* aStyleSet)
-  {
-    mPtr.mValue =
-      aStyleSet ? reinterpret_cast<uintptr_t>(aStyleSet) : 0;
-    return *this;
-  }
-
-  // Make StyleSetHandle usable in boolean contexts.
-  explicit operator bool() const { return !!mPtr.mValue; }
-  bool operator!() const { return !mPtr.mValue; }
-  bool operator==(const StyleSetHandle& aOth) const
-  {
-    return mPtr.mValue == aOth.mPtr.mValue;
-  }
-  bool operator!=(const StyleSetHandle& aOth) const { return !(*this == aOth); }
-
-  // Make StyleSetHandle behave like a smart pointer.
-  Ptr* operator->() { return &mPtr; }
-  const Ptr* operator->() const { return &mPtr; }
-
-private:
-  Ptr mPtr;
-};
-
-} // namespace mozilla
-
-#endif // mozilla_StyleSetHandle_h
diff --git a/layout/style/StyleSetHandleInlines.h b/layout/style/StyleSetHandleInlines.h
deleted file mode 100644
index b521de3aa995..000000000000
--- a/layout/style/StyleSetHandleInlines.h
+++ /dev/null
@@ -1,299 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#ifndef mozilla_StyleSetHandleInlines_h
-#define mozilla_StyleSetHandleInlines_h
-
-#include "mozilla/StyleSheetInlines.h"
-#include "mozilla/ComputedStyle.h"
-#include "mozilla/ServoStyleSet.h"
-#include "mozilla/ComputedStyle.h"
-
-
-#define FORWARD_CONCRETE(method_, geckoargs_, servoargs_) \
-  return AsServo()->method_ servoargs_;
-
-
-#define FORWARD(method_, args_) FORWARD_CONCRETE(method_, args_, args_)
-
-namespace mozilla {
-
-void
-StyleSetHandle::Ptr::Delete()
-{
-  if (mValue) {
-    delete AsServo();
-  }
-}
-
-void
-StyleSetHandle::Ptr::Init(nsPresContext* aPresContext)
-{
-  FORWARD(Init, (aPresContext));
-}
-
-void
-StyleSetHandle::Ptr::BeginShutdown()
-{
-  FORWARD(BeginShutdown, ());
-}
-
-void
-StyleSetHandle::Ptr::Shutdown()
-{
-  FORWARD(Shutdown, ());
-}
-
-bool
-StyleSetHandle::Ptr::GetAuthorStyleDisabled() const
-{
-  FORWARD(GetAuthorStyleDisabled, ());
-}
-
-void
-StyleSetHandle::Ptr::SetAuthorStyleDisabled(bool aStyleDisabled)
-{
-  FORWARD(SetAuthorStyleDisabled, (aStyleDisabled));
-}
-
-void
-StyleSetHandle::Ptr::BeginUpdate()
-{
-  FORWARD(BeginUpdate, ());
-}
-
-nsresult
-StyleSetHandle::Ptr::EndUpdate()
-{
-  FORWARD(EndUpdate, ());
-}
-
-// resolve a ComputedStyle
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveStyleFor(dom::Element* aElement,
-                                     ComputedStyle* aParentStyle,
-                                     LazyComputeBehavior aMayCompute)
-{
-  FORWARD(ResolveStyleFor, (aElement, aParentStyle, aMayCompute));
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveStyleForText(nsIContent* aTextNode,
-                                         ComputedStyle* aParentStyle)
-{
-  FORWARD(ResolveStyleForText, (aTextNode, aParentStyle));
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveStyleForPlaceholder()
-{
-  FORWARD(ResolveStyleForPlaceholder, ());
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveStyleForFirstLetterContinuation(ComputedStyle* aParentStyle)
-{
-  FORWARD(ResolveStyleForFirstLetterContinuation, (aParentStyle));
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolvePseudoElementStyle(dom::Element* aParentElement,
-                                               CSSPseudoElementType aType,
-                                               ComputedStyle* aParentStyle,
-                                               dom::Element* aPseudoElement)
-{
-  FORWARD(ResolvePseudoElementStyle, (aParentElement, aType, aParentStyle, aPseudoElement));
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveInheritingAnonymousBoxStyle(nsAtom* aPseudoTag,
-                                                        ComputedStyle* aParentStyle)
-{
-  FORWARD(ResolveInheritingAnonymousBoxStyle, (aPseudoTag, aParentStyle));
-}
-
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveNonInheritingAnonymousBoxStyle(nsAtom* aPseudoTag)
-{
-  FORWARD(ResolveNonInheritingAnonymousBoxStyle, (aPseudoTag));
-}
-
-#ifdef MOZ_XUL
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ResolveXULTreePseudoStyle(dom::Element* aParentElement,
-                                               nsICSSAnonBoxPseudo* aPseudoTag,
-                                               ComputedStyle* aParentStyle,
-                                               const AtomArray& aInputWord)
-{
-  FORWARD(ResolveXULTreePseudoStyle, (aParentElement, aPseudoTag, aParentStyle, aInputWord));
-}
-#endif
-
-// manage the set of style sheets in the style set
-nsresult
-StyleSetHandle::Ptr::AppendStyleSheet(SheetType aType, StyleSheet* aSheet)
-{
-  FORWARD_CONCRETE(AppendStyleSheet, (aType, aSheet->AsGecko()),
-                                     (aType, aSheet->AsServo()));
-}
-
-nsresult
-StyleSetHandle::Ptr::PrependStyleSheet(SheetType aType, StyleSheet* aSheet)
-{
-  FORWARD_CONCRETE(PrependStyleSheet, (aType, aSheet->AsGecko()),
-                                      (aType, aSheet->AsServo()));
-}
-
-nsresult
-StyleSetHandle::Ptr::RemoveStyleSheet(SheetType aType, StyleSheet* aSheet)
-{
-  FORWARD_CONCRETE(RemoveStyleSheet, (aType, aSheet->AsGecko()),
-                                     (aType, aSheet->AsServo()));
-}
-
-nsresult
-StyleSetHandle::Ptr::ReplaceSheets(SheetType aType,
-                       const nsTArray<RefPtr<StyleSheet>>& aNewSheets)
-{
-  nsTArray<RefPtr<ServoStyleSheet>> newSheets(aNewSheets.Length());
-  for (auto& sheet : aNewSheets) {
-    newSheets.AppendElement(sheet->AsServo());
-  }
-  return AsServo()->ReplaceSheets(aType, newSheets);
-}
-
-nsresult
-StyleSetHandle::Ptr::InsertStyleSheetBefore(SheetType aType,
-                                StyleSheet* aNewSheet,
-                                StyleSheet* aReferenceSheet)
-{
-  FORWARD_CONCRETE(
-    InsertStyleSheetBefore,
-    (aType, aNewSheet->AsGecko(), aReferenceSheet->AsGecko()),
-    (aType, aNewSheet->AsServo(), aReferenceSheet->AsServo()));
-}
-
-int32_t
-StyleSetHandle::Ptr::SheetCount(SheetType aType) const
-{
-  FORWARD(SheetCount, (aType));
-}
-
-StyleSheet*
-StyleSetHandle::Ptr::StyleSheetAt(SheetType aType, int32_t aIndex) const
-{
-  FORWARD(StyleSheetAt, (aType, aIndex));
-}
-
-void
-StyleSetHandle::Ptr::AppendAllXBLStyleSheets(nsTArray<StyleSheet*>& aArray) const
-{
-  FORWARD(AppendAllXBLStyleSheets, (aArray));
-}
-
-nsresult
-StyleSetHandle::Ptr::RemoveDocStyleSheet(StyleSheet* aSheet)
-{
-  FORWARD_CONCRETE(RemoveDocStyleSheet, (aSheet->AsGecko()),
-                                        (aSheet->AsServo()));
-}
-
-nsresult
-StyleSetHandle::Ptr::AddDocStyleSheet(StyleSheet* aSheet,
-                                      nsIDocument* aDocument)
-{
-  FORWARD_CONCRETE(AddDocStyleSheet, (aSheet->AsGecko(), aDocument),
-                                     (aSheet->AsServo(), aDocument));
-}
-
-void
-StyleSetHandle::Ptr::RuleRemoved(StyleSheet& aSheet, css::Rule& aRule)
-{
-  FORWARD_CONCRETE(RuleRemoved, (*aSheet.AsGecko(), aRule),
-                                (*aSheet.AsServo(), aRule));
-}
-
-void
-StyleSetHandle::Ptr::RuleAdded(StyleSheet& aSheet, css::Rule& aRule)
-{
-  FORWARD_CONCRETE(RuleAdded, (*aSheet.AsGecko(), aRule),
-                              (*aSheet.AsServo(), aRule));
-}
-
-void
-StyleSetHandle::Ptr::RuleChanged(StyleSheet& aSheet, css::Rule* aRule)
-{
-  FORWARD_CONCRETE(RuleChanged, (*aSheet.AsGecko(), aRule),
-                                (*aSheet.AsServo(), aRule));
-}
-
-void
-StyleSetHandle::Ptr::RecordShadowStyleChange(mozilla::dom::ShadowRoot& aShadowRoot)
-{
-  FORWARD(RecordShadowStyleChange, (aShadowRoot));
-}
-
-bool
-StyleSetHandle::Ptr::StyleSheetsHaveChanged() const
-{
-  FORWARD(StyleSheetsHaveChanged, ());
-}
-nsRestyleHint
-StyleSetHandle::Ptr::MediumFeaturesChanged(mozilla::MediaFeatureChangeReason aReason)
-{
-  FORWARD(MediumFeaturesChanged, (aReason));
-}
-void
-StyleSetHandle::Ptr::InvalidateStyleForCSSRuleChanges()
-{
-  FORWARD(InvalidateStyleForCSSRuleChanges, ());
-}
-
-// check whether there is ::before/::after style for an element
-already_AddRefed<ComputedStyle>
-StyleSetHandle::Ptr::ProbePseudoElementStyle(dom::Element* aParentElement,
-                                             CSSPseudoElementType aType,
-                                             ComputedStyle* aParentStyle)
-{
-  FORWARD(ProbePseudoElementStyle, (aParentElement, aType, aParentStyle));
-}
-
-bool
-StyleSetHandle::Ptr::
-AppendFontFaceRules(nsTArray<nsFontFaceRuleContainer>& aArray)
-{
-  FORWARD(AppendFontFaceRules, (aArray));
-}
-
-nsCSSCounterStyleRule*
-StyleSetHandle::Ptr::CounterStyleRuleForName(nsAtom* aName)
-{
-  FORWARD(CounterStyleRuleForName, (aName));
-}
-
-already_AddRefed<gfxFontFeatureValueSet>
-StyleSetHandle::Ptr::BuildFontFeatureValueSet()
-{
-  FORWARD(BuildFontFeatureValueSet, ());
-}
-
-bool
-StyleSetHandle::Ptr::EnsureUniqueInnerOnCSSSheets()
-{
-  FORWARD(EnsureUniqueInnerOnCSSSheets, ());
-}
-
-void
-StyleSetHandle::Ptr::SetNeedsRestyleAfterEnsureUniqueInner()
-{
-  FORWARD(SetNeedsRestyleAfterEnsureUniqueInner, ());
-}
-
-} // namespace mozilla
-
-#undef FORWARD
-
-#endif // mozilla_StyleSetHandleInlines_h
diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index 8526b7f07fce..39578362ddc1 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -17,7 +17,6 @@
 #include "mozilla/ServoCSSRuleList.h"
 #include "mozilla/ServoStyleSet.h"
 #include "mozilla/ServoStyleSheet.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "mozilla/StyleSheetInlines.h"
 
 #include "mozAutoDocUpdate.h"
@@ -360,7 +359,7 @@ StyleSheet::WillDirty()
 }
 
 void
-StyleSheet::AddStyleSet(const StyleSetHandle& aStyleSet)
+StyleSheet::AddStyleSet(ServoStyleSet* aStyleSet)
 {
   NS_ASSERTION(!mStyleSets.Contains(aStyleSet),
                "style set already registered");
@@ -368,7 +367,7 @@ StyleSheet::AddStyleSet(const StyleSetHandle& aStyleSet)
 }
 
 void
-StyleSheet::DropStyleSet(const StyleSetHandle& aStyleSet)
+StyleSheet::DropStyleSet(ServoStyleSet* aStyleSet)
 {
   DebugOnly<bool> found = mStyleSets.RemoveElement(aStyleSet);
   NS_ASSERTION(found, "didn't find style set");
@@ -399,7 +398,7 @@ StyleSheet::EnsureUniqueInner()
   // let our containing style sets know that if we call
   // nsPresContext::EnsureSafeToHandOutCSSRules we will need to restyle the
   // document
-  for (StyleSetHandle& setHandle : mStyleSets) {
+  for (ServoStyleSet* setHandle : mStyleSets) {
     setHandle->SetNeedsRestyleAfterEnsureUniqueInner();
   }
 }
@@ -527,7 +526,7 @@ StyleSheet::GetContainingShadow() const
 #define NOTIFY(function_, args_) do {                     \
   StyleSheet* current = this;                             \
   do {                                                    \
-    for (StyleSetHandle handle : current->mStyleSets) {   \
+    for (ServoStyleSet* handle : current->mStyleSets) {   \
       handle->function_ args_;                            \
     }                                                     \
     if (auto* shadow = current->GetContainingShadow()) {  \
@@ -542,7 +541,7 @@ StyleSheet::RuleAdded(css::Rule& aRule)
 {
   DidDirty();
   mDirtyFlags |= MODIFIED_RULES;
-  NOTIFY(RuleAdded, (*this, aRule));
+  NOTIFY(RuleAdded, (*AsServo(), aRule));
 
   if (mDocument) {
     mDocument->StyleRuleAdded(this, &aRule);
@@ -554,7 +553,7 @@ StyleSheet::RuleRemoved(css::Rule& aRule)
 {
   DidDirty();
   mDirtyFlags |= MODIFIED_RULES;
-  NOTIFY(RuleRemoved, (*this, aRule));
+  NOTIFY(RuleRemoved, (*AsServo(), aRule));
 
   if (mDocument) {
     mDocument->StyleRuleRemoved(this, &aRule);
@@ -566,7 +565,7 @@ StyleSheet::RuleChanged(css::Rule* aRule)
 {
   DidDirty();
   mDirtyFlags |= MODIFIED_RULES;
-  NOTIFY(RuleChanged, (*this, aRule));
+  NOTIFY(RuleChanged, (*AsServo(), aRule));
 
   if (mDocument) {
     mDocument->StyleRuleChanged(this, aRule);
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index a15f9d697e20..bce562bf5980 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -23,8 +23,8 @@ class nsCSSRuleProcessor;
 namespace mozilla {
 
 class CSSStyleSheet;
+class ServoStyleSet;
 class ServoStyleSheet;
-class StyleSetHandle;
 struct StyleSheetInfo;
 struct CSSStyleSheetInner;
 
@@ -260,8 +260,8 @@ class StyleSheet : public nsICSSLoaderObserver
   // it's owning media rule, plus it's used for the stylesheet media itself.
   void RuleChanged(css::Rule*);
 
-  void AddStyleSet(const StyleSetHandle& aStyleSet);
-  void DropStyleSet(const StyleSetHandle& aStyleSet);
+  void AddStyleSet(ServoStyleSet* aStyleSet);
+  void DropStyleSet(ServoStyleSet* aStyleSet);
 
   nsresult DeleteRuleFromGroup(css::GroupRule* aGroup, uint32_t aIndex);
   nsresult InsertRuleIntoGroup(const nsAString& aRule,
@@ -369,7 +369,7 @@ class StyleSheet : public nsICSSLoaderObserver
   // StyleSheet clones.
   StyleSheetInfo* mInner;
 
-  nsTArray<StyleSetHandle> mStyleSets;
+  nsTArray<ServoStyleSet*> mStyleSets;
 
   friend class ::nsCSSRuleProcessor;
 
diff --git a/layout/style/moz.build b/layout/style/moz.build
index b57fe3a05458..6b0f482cbc59 100644
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@@ -112,8 +112,6 @@ EXPORTS.mozilla += [
     'StyleAnimationValue.h',
     'StyleComplexColor.h',
     'StylePrefs.h',
-    'StyleSetHandle.h',
-    'StyleSetHandleInlines.h',
     'StyleSheet.h',
     'StyleSheetInfo.h',
     'StyleSheetInlines.h',
diff --git a/layout/style/nsAnimationManager.cpp b/layout/style/nsAnimationManager.cpp
index 573a0160bd26..45dbe393bab8 100755
--- a/layout/style/nsAnimationManager.cpp
+++ b/layout/style/nsAnimationManager.cpp
@@ -362,7 +362,7 @@ class MOZ_STACK_CLASS ServoCSSAnimationBuilder final {
                       const nsTimingFunction& aTimingFunction,
                       nsTArray<Keyframe>& aKeyframes)
   {
-    ServoStyleSet* styleSet = aPresContext->StyleSet()->AsServo();
+    ServoStyleSet* styleSet = aPresContext->StyleSet();
     MOZ_ASSERT(styleSet);
     return styleSet->GetKeyframesForName(aName,
                                          aTimingFunction,
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 3662a03a9e74..15175c1e0528 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -37,8 +37,7 @@
 #include "nsCSSPseudoElements.h"
 #include "mozilla/EffectSet.h"
 #include "mozilla/IntegerRange.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/ServoRestyleManager.h"
 #include "mozilla/RestyleManagerInlines.h"
 #include "imgIRequest.h"
@@ -120,7 +119,7 @@ DocumentNeedsRestyle(
 
   // Unfortunately we don't know if the sheet change affects mContent or not, so
   // just assume it will and that we need to flush normally.
-  StyleSetHandle styleSet = shell->StyleSet();
+  ServoStyleSet* styleSet = shell->StyleSet();
   if (styleSet->StyleSheetsHaveChanged()) {
     return true;
   }
@@ -550,7 +549,7 @@ nsComputedDOMStyle::DoGetComputedStyleNoFlush(Element* aElement,
 
   // No frame has been created, or we have a pseudo, or we're looking
   // for the default style, so resolve the style ourselves.
-  ServoStyleSet* styleSet = presShell->StyleSet()->AsServo();
+  ServoStyleSet* styleSet = presShell->StyleSet();
 
   StyleRuleInclusion rules = aStyleType == eDefaultOnly
                              ? StyleRuleInclusion::DefaultOnly
@@ -579,8 +578,8 @@ nsComputedDOMStyle::GetUnanimatedComputedStyleNoFlush(Element* aElement,
     return nullptr;
   }
 
-  return shell->StyleSet()->AsServo()->GetBaseContextForElement(
-    elementOrPseudoElement, style);
+  return shell->StyleSet()->
+    GetBaseContextForElement(elementOrPseudoElement, style);
 }
 
 nsMargin
diff --git a/layout/style/nsStyleStructInlines.h b/layout/style/nsStyleStructInlines.h
index 3ad1151e1f10..5e0fd1accf04 100644
--- a/layout/style/nsStyleStructInlines.h
+++ b/layout/style/nsStyleStructInlines.h
@@ -17,7 +17,6 @@
 #include "nsIContent.h" // for GetParent()
 #include "nsTextFrame.h" // for nsTextFrame::ShouldSuppressLineBreak
 #include "nsSVGUtils.h" // for nsSVGUtils::IsInSVGTextSubtree
-#include "mozilla/ServoStyleSet.h"
 
 inline void
 nsStyleImage::EnsureCachedBIData() const
diff --git a/layout/tables/nsTableFrame.cpp b/layout/tables/nsTableFrame.cpp
index 3d2b8ffee95d..95234407594e 100644
--- a/layout/tables/nsTableFrame.cpp
+++ b/layout/tables/nsTableFrame.cpp
@@ -41,8 +41,6 @@
 #include "mozilla/Range.h"
 #include "mozilla/ServoRestyleManager.h"
 #include "mozilla/ServoStyleSet.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsDisplayList.h"
 #include "nsIScrollableFrame.h"
 #include "nsCSSProps.h"
diff --git a/layout/xul/nsListBoxBodyFrame.cpp b/layout/xul/nsListBoxBodyFrame.cpp
index 2dca3a208820..c320d9505add 100644
--- a/layout/xul/nsListBoxBodyFrame.cpp
+++ b/layout/xul/nsListBoxBodyFrame.cpp
@@ -26,8 +26,7 @@
 #include "mozilla/ComputedStyle.h"
 #include "nsFontMetrics.h"
 #include "nsITimer.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 #include "mozilla/dom/Text.h"
 #include "nsPIBoxObject.h"
 #include "nsLayoutUtils.h"
diff --git a/layout/xul/nsSplitterFrame.cpp b/layout/xul/nsSplitterFrame.cpp
index 4eb826befeaa..4cd3819b8a83 100644
--- a/layout/xul/nsSplitterFrame.cpp
+++ b/layout/xul/nsSplitterFrame.cpp
@@ -29,8 +29,6 @@
 #include "nsIServiceManager.h"
 #include "nsContainerFrame.h"
 #include "nsContentCID.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
 #include "nsLayoutUtils.h"
 #include "nsDisplayList.h"
 #include "nsContentUtils.h"
diff --git a/layout/xul/tree/nsTreeStyleCache.cpp b/layout/xul/tree/nsTreeStyleCache.cpp
index e63368d23b48..5149e7d0e8f4 100644
--- a/layout/xul/tree/nsTreeStyleCache.cpp
+++ b/layout/xul/tree/nsTreeStyleCache.cpp
@@ -6,8 +6,7 @@
 
 #include "nsTreeStyleCache.h"
 #include "mozilla/dom/Element.h"
-#include "mozilla/StyleSetHandle.h"
-#include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/ServoStyleSet.h"
 
 using namespace mozilla;