diff --git a/packages/react-devtools-scheduling-profiler/package.json b/packages/react-devtools-scheduling-profiler/package.json
index 5aa14a59f0df9..ca2b39d40da83 100644
--- a/packages/react-devtools-scheduling-profiler/package.json
+++ b/packages/react-devtools-scheduling-profiler/package.json
@@ -28,6 +28,7 @@
     "url-loader": "^4.1.0",
     "webpack": "^4.44.1",
     "webpack-cli": "^3.3.12",
-    "webpack-dev-server": "^3.11.0"
+    "webpack-dev-server": "^3.11.0",
+    "worker-loader": "^3.0.2"
   }
 }
diff --git a/packages/react-devtools-scheduling-profiler/src/App.js b/packages/react-devtools-scheduling-profiler/src/App.js
index 83d9238851344..9a27253b6c032 100644
--- a/packages/react-devtools-scheduling-profiler/src/App.js
+++ b/packages/react-devtools-scheduling-profiler/src/App.js
@@ -14,23 +14,21 @@ import '@reach/tooltip/styles.css';
 
 import * as React from 'react';
 
-import {ModalDialogContextController} from 'react-devtools-shared/src/devtools/views/ModalDialog';
 import {SchedulingProfiler} from './SchedulingProfiler';
-import {useBrowserTheme} from './hooks';
+import {useBrowserTheme, useDisplayDensity} from './hooks';
 
 import styles from './App.css';
 import 'react-devtools-shared/src/devtools/views/root.css';
 
 export default function App() {
   useBrowserTheme();
+  useDisplayDensity();
 
   return (
-    <ModalDialogContextController>
-      <div className={styles.DevTools}>
-        <div className={styles.TabContent}>
-          <SchedulingProfiler />
-        </div>
+    <div className={styles.DevTools}>
+      <div className={styles.TabContent}>
+        <SchedulingProfiler />
       </div>
-    </ModalDialogContextController>
+    </div>
   );
 }
diff --git a/packages/react-devtools-scheduling-profiler/src/ImportButton.css b/packages/react-devtools-scheduling-profiler/src/ImportButton.css
index f0cb09ef4df38..e9054b7749692 100644
--- a/packages/react-devtools-scheduling-profiler/src/ImportButton.css
+++ b/packages/react-devtools-scheduling-profiler/src/ImportButton.css
@@ -8,10 +8,3 @@
   overflow: hidden;
   clip: rect(1px, 1px, 1px, 1px);
 }
-
-.ErrorMessage {
-  margin: 0.5rem 0;
-  color: var(--color-dim);
-  font-family: var(--font-family-monospace);
-  font-size: var(--font-size-monospace-normal);
-}
diff --git a/packages/react-devtools-scheduling-profiler/src/ImportButton.js b/packages/react-devtools-scheduling-profiler/src/ImportButton.js
index 2f6ba344a07e3..acd382b08ad05 100644
--- a/packages/react-devtools-scheduling-profiler/src/ImportButton.js
+++ b/packages/react-devtools-scheduling-profiler/src/ImportButton.js
@@ -7,61 +7,32 @@
  * @flow
  */
 
-import type {TimelineEvent} from '@elg/speedscope';
-import type {ReactProfilerData} from './types';
-
 import * as React from 'react';
-import {useCallback, useContext, useRef} from 'react';
+import {useCallback, useRef} from 'react';
 
 import Button from 'react-devtools-shared/src/devtools/views/Button';
 import ButtonIcon from 'react-devtools-shared/src/devtools/views/ButtonIcon';
-import {ModalDialogContext} from 'react-devtools-shared/src/devtools/views/ModalDialog';
-
-import preprocessData from './utils/preprocessData';
-import {readInputData} from './utils/readInputData';
 
 import styles from './ImportButton.css';
 
 type Props = {|
-  onDataImported: (profilerData: ReactProfilerData) => void,
+  onFileSelect: (file: File) => void,
 |};
 
-export default function ImportButton({onDataImported}: Props) {
+export default function ImportButton({onFileSelect}: Props) {
   const inputRef = useRef<HTMLInputElement | null>(null);
-  const {dispatch: modalDialogDispatch} = useContext(ModalDialogContext);
 
-  const handleFiles = useCallback(async () => {
+  const handleFiles = useCallback(() => {
     const input = inputRef.current;
     if (input === null) {
       return;
     }
-
     if (input.files.length > 0) {
-      try {
-        const readFile = await readInputData(input.files[0]);
-        const events: TimelineEvent[] = JSON.parse(readFile);
-        if (events.length > 0) {
-          onDataImported(preprocessData(events));
-        }
-      } catch (error) {
-        modalDialogDispatch({
-          type: 'SHOW',
-          title: 'Import failed',
-          content: (
-            <>
-              <div>The profiling data you selected cannot be imported.</div>
-              {error !== null && (
-                <div className={styles.ErrorMessage}>{error.message}</div>
-              )}
-            </>
-          ),
-        });
-      }
+      onFileSelect(input.files[0]);
     }
-
     // Reset input element to allow the same file to be re-imported
     input.value = '';
-  }, [onDataImported, modalDialogDispatch]);
+  }, [onFileSelect]);
 
   const uploadData = useCallback(() => {
     if (inputRef.current !== null) {
diff --git a/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.css b/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.css
index b734a25e1ea83..e16279192b83e 100644
--- a/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.css
+++ b/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.css
@@ -28,6 +28,13 @@
   text-align: center;
 }
 
+.ErrorMessage {
+  margin: 0.5rem 0;
+  color: var(--color-dim);
+  font-family: var(--font-family-monospace);
+  font-size: var(--font-size-monospace-normal);
+}
+
 .Row {
   display: flex;
   flex-direction: row;
diff --git a/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.js b/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.js
index 19079a4990776..2f232b6bbe183 100644
--- a/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.js
+++ b/packages/react-devtools-scheduling-profiler/src/SchedulingProfiler.js
@@ -7,30 +7,60 @@
  * @flow
  */
 
+import type {Resource} from 'react-devtools-shared/src/devtools/cache';
 import type {ReactProfilerData} from './types';
+import type {ImportWorkerOutputData} from './import-worker/import.worker';
 
 import * as React from 'react';
-import {useState} from 'react';
-
-import ImportButton from './ImportButton';
-import {ModalDialog} from 'react-devtools-shared/src/devtools/views/ModalDialog';
+import {Suspense, useCallback, useState} from 'react';
+import {createResource} from 'react-devtools-shared/src/devtools/cache';
 import ReactLogo from 'react-devtools-shared/src/devtools/views/ReactLogo';
 
+import ImportButton from './ImportButton';
 import CanvasPage from './CanvasPage';
+import ImportWorker from './import-worker/import.worker';
 
 import profilerBrowser from './assets/profilerBrowser.png';
 import styles from './SchedulingProfiler.css';
 
-export function SchedulingProfiler(_: {||}) {
-  const [profilerData, setProfilerData] = useState<ReactProfilerData | null>(
-    null,
-  );
+type DataResource = Resource<void, File, ReactProfilerData | Error>;
+
+function createDataResourceFromImportedFile(file: File): DataResource {
+  return createResource(
+    () => {
+      return new Promise<ReactProfilerData | Error>((resolve, reject) => {
+        const worker: Worker = new (ImportWorker: any)();
 
-  const view = profilerData ? (
-    <CanvasPage profilerData={profilerData} />
-  ) : (
-    <Welcome onDataImported={setProfilerData} />
+        worker.onmessage = function(event) {
+          const data = ((event.data: any): ImportWorkerOutputData);
+          switch (data.status) {
+            case 'SUCCESS':
+              resolve(data.processedData);
+              break;
+            case 'INVALID_PROFILE_ERROR':
+              resolve(data.error);
+              break;
+            case 'UNEXPECTED_ERROR':
+              reject(data.error);
+              break;
+          }
+          worker.terminate();
+        };
+
+        worker.postMessage({file});
+      });
+    },
+    () => file,
+    {useWeakMap: true},
   );
+}
+
+export function SchedulingProfiler(_: {||}) {
+  const [dataResource, setDataResource] = useState<DataResource | null>(null);
+
+  const handleFileSelect = useCallback((file: File) => {
+    setDataResource(createDataResourceFromImportedFile(file));
+  }, []);
 
   return (
     <div className={styles.SchedulingProfiler}>
@@ -38,22 +68,26 @@ export function SchedulingProfiler(_: {||}) {
         <ReactLogo />
         <span className={styles.AppName}>Concurrent Mode Profiler</span>
         <div className={styles.VRule} />
-        <ImportButton onDataImported={setProfilerData} />
+        <ImportButton onFileSelect={handleFileSelect} />
         <div className={styles.Spacer} />
       </div>
       <div className={styles.Content}>
-        {view}
-        <ModalDialog />
+        {dataResource ? (
+          <Suspense fallback={<ProcessingData />}>
+            <DataResourceComponent
+              dataResource={dataResource}
+              onFileSelect={handleFileSelect}
+            />
+          </Suspense>
+        ) : (
+          <Welcome onFileSelect={handleFileSelect} />
+        )}
       </div>
     </div>
   );
 }
 
-type WelcomeProps = {|
-  onDataImported: (profilerData: ReactProfilerData) => void,
-|};
-
-const Welcome = ({onDataImported}: WelcomeProps) => (
+const Welcome = ({onFileSelect}: {|onFileSelect: (file: File) => void|}) => (
   <div className={styles.EmptyStateContainer}>
     <div className={styles.ScreenshotWrapper}>
       <img
@@ -65,8 +99,47 @@ const Welcome = ({onDataImported}: WelcomeProps) => (
     <div className={styles.Header}>Welcome!</div>
     <div className={styles.Row}>
       Click the import button
-      <ImportButton onDataImported={onDataImported} /> to import a Chrome
+      <ImportButton onFileSelect={onFileSelect} /> to import a Chrome
       performance profile.
     </div>
   </div>
 );
+
+const ProcessingData = () => (
+  <div className={styles.EmptyStateContainer}>
+    <div className={styles.Header}>Processing data...</div>
+    <div className={styles.Row}>This should only take a minute.</div>
+  </div>
+);
+
+const CouldNotLoadProfile = ({error, onFileSelect}) => (
+  <div className={styles.EmptyStateContainer}>
+    <div className={styles.Header}>Could not load profile</div>
+    {error.message && (
+      <div className={styles.Row}>
+        <div className={styles.ErrorMessage}>{error.message}</div>
+      </div>
+    )}
+    <div className={styles.Row}>
+      Try importing
+      <ImportButton onFileSelect={onFileSelect} />
+      another Chrome performance profile.
+    </div>
+  </div>
+);
+
+const DataResourceComponent = ({
+  dataResource,
+  onFileSelect,
+}: {|
+  dataResource: DataResource,
+  onFileSelect: (file: File) => void,
+|}) => {
+  const dataOrError = dataResource.read();
+  if (dataOrError instanceof Error) {
+    return (
+      <CouldNotLoadProfile error={dataOrError} onFileSelect={onFileSelect} />
+    );
+  }
+  return <CanvasPage profilerData={dataOrError} />;
+};
diff --git a/packages/react-devtools-scheduling-profiler/src/hooks.js b/packages/react-devtools-scheduling-profiler/src/hooks.js
index 13bd7508a288e..6096d6b950546 100644
--- a/packages/react-devtools-scheduling-profiler/src/hooks.js
+++ b/packages/react-devtools-scheduling-profiler/src/hooks.js
@@ -13,7 +13,10 @@ import {
   useLayoutEffect,
 } from 'react';
 
-import {updateThemeVariables} from 'react-devtools-shared/src/devtools/views/Settings/SettingsContext';
+import {
+  updateDisplayDensity,
+  updateThemeVariables,
+} from 'react-devtools-shared/src/devtools/views/Settings/SettingsContext';
 import {enableDarkMode} from './SchedulingProfilerFeatureFlags';
 
 export type BrowserTheme = 'dark' | 'light';
@@ -57,3 +60,10 @@ export function useBrowserTheme(): void {
     }
   }, [theme]);
 }
+
+export function useDisplayDensity(): void {
+  useLayoutEffect(() => {
+    const documentElements = [((document.documentElement: any): HTMLElement)];
+    updateDisplayDensity('comfortable', documentElements);
+  }, []);
+}
diff --git a/packages/react-devtools-scheduling-profiler/src/import-worker/InvalidProfileError.js b/packages/react-devtools-scheduling-profiler/src/import-worker/InvalidProfileError.js
new file mode 100644
index 0000000000000..a6c31c941c110
--- /dev/null
+++ b/packages/react-devtools-scheduling-profiler/src/import-worker/InvalidProfileError.js
@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+/**
+ * An error thrown when an invalid profile could not be processed.
+ */
+export default class InvalidProfileError extends Error {}
diff --git a/packages/react-devtools-scheduling-profiler/src/utils/__tests__/__snapshots__/preprocessData-test.js.snap b/packages/react-devtools-scheduling-profiler/src/import-worker/__tests__/__snapshots__/preprocessData-test.js.snap
similarity index 100%
rename from packages/react-devtools-scheduling-profiler/src/utils/__tests__/__snapshots__/preprocessData-test.js.snap
rename to packages/react-devtools-scheduling-profiler/src/import-worker/__tests__/__snapshots__/preprocessData-test.js.snap
diff --git a/packages/react-devtools-scheduling-profiler/src/utils/__tests__/preprocessData-test.js b/packages/react-devtools-scheduling-profiler/src/import-worker/__tests__/preprocessData-test.js
similarity index 100%
rename from packages/react-devtools-scheduling-profiler/src/utils/__tests__/preprocessData-test.js
rename to packages/react-devtools-scheduling-profiler/src/import-worker/__tests__/preprocessData-test.js
diff --git a/packages/react-devtools-scheduling-profiler/src/import-worker/import.worker.js b/packages/react-devtools-scheduling-profiler/src/import-worker/import.worker.js
new file mode 100644
index 0000000000000..118490e2effe5
--- /dev/null
+++ b/packages/react-devtools-scheduling-profiler/src/import-worker/import.worker.js
@@ -0,0 +1,57 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import 'regenerator-runtime/runtime';
+
+import type {TimelineEvent} from '@elg/speedscope';
+import type {ReactProfilerData} from '../types';
+
+import preprocessData from './preprocessData';
+import {readInputData} from './readInputData';
+import InvalidProfileError from './InvalidProfileError';
+
+declare var self: DedicatedWorkerGlobalScope;
+
+type ImportWorkerInputData = {|
+  file: File,
+|};
+
+export type ImportWorkerOutputData =
+  | {|status: 'SUCCESS', processedData: ReactProfilerData|}
+  | {|status: 'INVALID_PROFILE_ERROR', error: Error|}
+  | {|status: 'UNEXPECTED_ERROR', error: Error|};
+
+self.onmessage = async function(event: MessageEvent) {
+  const {file} = ((event.data: any): ImportWorkerInputData);
+
+  try {
+    const readFile = await readInputData(file);
+    const events: TimelineEvent[] = JSON.parse(readFile);
+    if (events.length === 0) {
+      throw new InvalidProfileError('No profiling data found in file.');
+    }
+
+    self.postMessage({
+      status: 'SUCCESS',
+      processedData: preprocessData(events),
+    });
+  } catch (error) {
+    if (error instanceof InvalidProfileError) {
+      self.postMessage({
+        status: 'INVALID_PROFILE_ERROR',
+        error,
+      });
+    } else {
+      self.postMessage({
+        status: 'UNEXPECTED_ERROR',
+        error,
+      });
+    }
+  }
+};
diff --git a/packages/react-devtools-scheduling-profiler/src/utils/preprocessData.js b/packages/react-devtools-scheduling-profiler/src/import-worker/preprocessData.js
similarity index 96%
rename from packages/react-devtools-scheduling-profiler/src/utils/preprocessData.js
rename to packages/react-devtools-scheduling-profiler/src/import-worker/preprocessData.js
index 402ff9ea15756..e5239fd78d1fa 100644
--- a/packages/react-devtools-scheduling-profiler/src/utils/preprocessData.js
+++ b/packages/react-devtools-scheduling-profiler/src/import-worker/preprocessData.js
@@ -22,6 +22,7 @@ import type {
 } from '../types';
 
 import {REACT_TOTAL_NUM_LANES} from '../constants';
+import InvalidProfileError from './InvalidProfileError';
 
 type MeasureStackElement = {|
   type: ReactMeasureType,
@@ -144,7 +145,7 @@ function throwIfIncomplete(
   if (lastIndex >= 0) {
     const last = stack[lastIndex];
     if (last.stopTime === undefined && last.type === type) {
-      throw new Error(
+      throw new InvalidProfileError(
         `Unexpected type "${type}" started before "${last.type}" completed.`,
       );
     }
@@ -369,7 +370,7 @@ function processTimelineEvent(
 
   // Unrecognized event
   else {
-    throw new Error(
+    throw new InvalidProfileError(
       `Unrecognized event ${JSON.stringify(
         event,
       )}! This is likely a bug in this profiler tool.`,
@@ -378,7 +379,16 @@ function processTimelineEvent(
 }
 
 function preprocessFlamechart(rawData: TimelineEvent[]): Flamechart {
-  const parsedData = importFromChromeTimeline(rawData, 'react-devtools');
+  let parsedData;
+  try {
+    parsedData = importFromChromeTimeline(rawData, 'react-devtools');
+  } catch (error) {
+    // Assume any Speedscope errors are caused by bad profiles
+    const errorToRethrow = new InvalidProfileError(error.message);
+    errorToRethrow.stack = error.stack;
+    throw errorToRethrow;
+  }
+
   const profile = parsedData.profiles[0]; // TODO: Choose the main CPU thread only
 
   const speedscopeFlamechart = new SpeedscopeFlamechart({
diff --git a/packages/react-devtools-scheduling-profiler/src/utils/readInputData.js b/packages/react-devtools-scheduling-profiler/src/import-worker/readInputData.js
similarity index 74%
rename from packages/react-devtools-scheduling-profiler/src/utils/readInputData.js
rename to packages/react-devtools-scheduling-profiler/src/import-worker/readInputData.js
index fe46337f0f0e1..2280e269961bb 100644
--- a/packages/react-devtools-scheduling-profiler/src/utils/readInputData.js
+++ b/packages/react-devtools-scheduling-profiler/src/import-worker/readInputData.js
@@ -8,13 +8,12 @@
  */
 
 import nullthrows from 'nullthrows';
+import InvalidProfileError from './InvalidProfileError';
 
 export const readInputData = (file: File): Promise<string> => {
   if (!file.name.endsWith('.json')) {
-    return Promise.reject(
-      new Error(
-        'Invalid file type. Only JSON performance profiles are supported',
-      ),
+    throw new InvalidProfileError(
+      'Invalid file type. Only JSON performance profiles are supported',
     );
   }
 
@@ -26,7 +25,7 @@ export const readInputData = (file: File): Promise<string> => {
       if (typeof result === 'string') {
         resolve(result);
       }
-      reject(new Error('Input file was not read as a string'));
+      reject(new InvalidProfileError('Input file was not read as a string'));
     };
 
     fileReader.onerror = () => reject(fileReader.error);
diff --git a/packages/react-devtools-scheduling-profiler/webpack.config.js b/packages/react-devtools-scheduling-profiler/webpack.config.js
index 60d6e4467f7d3..6f7028eea26c3 100644
--- a/packages/react-devtools-scheduling-profiler/webpack.config.js
+++ b/packages/react-devtools-scheduling-profiler/webpack.config.js
@@ -26,6 +26,18 @@ const DEVTOOLS_VERSION = getVersionString();
 
 const imageInlineSizeLimit = 10000;
 
+const babelOptions = {
+  configFile: resolve(
+    __dirname,
+    '..',
+    'react-devtools-shared',
+    'babel.config.js',
+  ),
+  plugins: shouldUseDevServer
+    ? [resolve(builtModulesDir, 'react-refresh/babel')]
+    : [],
+};
+
 const config = {
   mode: __DEV__ ? 'development' : 'production',
   devtool: __DEV__ ? 'cheap-module-eval-source-map' : false,
@@ -53,20 +65,20 @@ const config = {
   ].filter(Boolean),
   module: {
     rules: [
+      {
+        test: /\.worker\.js$/,
+        use: [
+          'worker-loader',
+          {
+            loader: 'babel-loader',
+            options: babelOptions,
+          },
+        ],
+      },
       {
         test: /\.js$/,
         loader: 'babel-loader',
-        options: {
-          configFile: resolve(
-            __dirname,
-            '..',
-            'react-devtools-shared',
-            'babel.config.js',
-          ),
-          plugins: shouldUseDevServer
-            ? [resolve(builtModulesDir, 'react-refresh/babel')]
-            : [],
-        },
+        options: babelOptions,
       },
       {
         test: /\.css$/,
diff --git a/packages/react-devtools-shared/src/devtools/views/Settings/SettingsContext.js b/packages/react-devtools-shared/src/devtools/views/Settings/SettingsContext.js
index d13fc31b57fc2..2a89a9fe679b7 100644
--- a/packages/react-devtools-shared/src/devtools/views/Settings/SettingsContext.js
+++ b/packages/react-devtools-shared/src/devtools/views/Settings/SettingsContext.js
@@ -214,7 +214,7 @@ function updateStyleHelper(
   );
 }
 
-function updateDisplayDensity(
+export function updateDisplayDensity(
   displayDensity: DisplayDensity,
   documentElements: DocumentElements,
 ): void {
diff --git a/yarn.lock b/yarn.lock
index 1916f50052d8c..851c8908e5331 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -14102,6 +14102,14 @@ worker-farm@^1.7.0:
   dependencies:
     errno "~0.1.7"
 
+worker-loader@^3.0.2:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/worker-loader/-/worker-loader-3.0.2.tgz#f82386a96366d24dbf6c2420f5bed04d3fe5a229"
+  integrity sha512-a3Hk9/3OCKkiK00gRIenNd4pdwBQn2Hu2L39WPGqR5WlX90u++mAVK7K1i6zUQyio4zqpnaastJ7J0xCBaA3VA==
+  dependencies:
+    loader-utils "^2.0.0"
+    schema-utils "^2.7.0"
+
 wrap-ansi@^2.0.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/wrap-ansi/-/wrap-ansi-2.1.0.tgz#d8fc3d284dd05794fe84973caecdd1cf824fdd85"