added the experimental release notes

files/en-us/mozilla/firefox/experimental_features/index.md

@@ -463,6 +463,21 @@ The default behavior of named timeline scoping has been updated to be global. Th
 - `layout.css.scroll-driven-animations.enabled`
   - : Set to `true` to enable.
 
+### `named-feature()` support queries
+
+The `named-feature()` function in the {{cssxref("@supports")}} at-rule lets you test whether the browser supports a feature that has no other detectable syntax, for example `@supports named-feature(anchor-position-follows-transforms)`.
+([Firefox bug 2042977](https://bugzil.la/2042977) and [Firefox bug 2055354](https://bugzil.la/2055354)).
+
+| Release channel   | Version added | Enabled by default? |
+| ----------------- | ------------- | ------------------- |
+| Nightly           | 156           | No                  |
+| Developer Edition | 156           | No                  |
+| Beta              | 156           | No                  |
+| Release           | 156           | No                  |
+
+- `layout.css.supports.at-rule.enabled`
+  - : Set to `true` to enable.
+
 ## SVG
 
 **No experimental features in this release cycle.**
@@ -494,6 +509,22 @@ When enabled, the MathML [`<a>`](/en-US/docs/Web/MathML/Reference/Element/a) ele
 | Beta              | 155           | No                  |
 | Release           | 155           | No                  |
 
+- `mathml.a.element.enabled`
+  - : Set to `true` to enable.
+
+### MathML `<a>` elements
+
+The MathML `<a>` element creates a hyperlink from MathML content, exposing the `MathMLAnchorElement` interface with the same URL component properties as HTML {{HTMLElement("a")}} elements.
+
+This release adds support for the `rel` and `relList` IDL attributes. ([Firefox bug 2063819](https://bugzil.la/2063819)).
+
+| Release channel   | Version added | Enabled by default? |
+| ----------------- | ------------- | ------------------- |
+| Nightly           | 156           | Yes                 |
+| Developer Edition | 156           | No                  |
+| Beta              | 156           | No                  |
+| Release           | 156           | No                  |
+
 - `mathml.a.element.enabled`
   - : Set to `true` to enable.
 
@@ -575,9 +606,11 @@ This can be used to avoid collisions where multiple web components declare eleme
 The implementation includes:
 
 - `customElementRegistry` property on {{domxref("Document")}}, {{domxref("Element")}}, and {{domxref("ShadowRoot")}}.
-  The [`CustomElementRegistry()` constructor](/en-US/docs/Web/API/CustomElementRegistry/CustomElementRegistry) creates a new `CustomElementRegistry` object for scoped usage.
+  The [`CustomElementRegistry()` constructor](/en-US/docs/Web/API/CustomElementRegistry/CustomElementRegistry) creates a new `CustomElementRegistry` object for scoped usage. ([Firefox bug 2018900](https://bugzil.la/2018900))
+
+From version 156:
 
-  ([Firefox bug 2018900](https://bugzil.la/2018900)).
+- [Scoped custom element registries](/en-US/docs/Web/API/Web_components/Using_custom_elements#scoped_custom_element_registries) are now supported, so that a shadow root can define custom elements that do not clash with those defined in the global registry. ([Firefox bug 2064333](https://bugzil.la/2064333)).
 
 | Release channel   | Version added | Enabled by default? |
 | ----------------- | ------------- | ------------------- |
@@ -802,6 +835,21 @@ Notifications have the [`requireInteraction`](/en-US/docs/Web/API/Notification/r
 - `dom.webnotifications.requireinteraction.enabled`
   - : Set to `true` to enable.
 
+### Container Timing API
+
+The Container Timing API reports when the contents of a container element are painted, letting you measure the render time of a region of the page rather than of the whole viewport.
+([Firefox bug 1940240](https://bugzil.la/1940240)).
+
+| Release channel   | Version changed | Enabled by default? |
+| ----------------- | --------------- | ------------------- |
+| Nightly           | 156             | No                  |
+| Developer Edition | 156             | No                  |
+| Beta              | 156             | No                  |
+| Release           | 156             | No                  |
+
+- `dom.enable_container_timing`
+  - : Set to `true` to enable.
+
 ## Security and privacy
 
 ### Insecure page labeling