added release note for Namespaced attributes in attr() (#43789)

* added release not for Namespaced attributes in attr()

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

Co-authored-by: Vadim Makeev <hi@pepelsbey.dev>

* Update files/en-us/mozilla/firefox/releases/150/index.md

Co-authored-by: Vadim Makeev <hi@pepelsbey.dev>

---------

Co-authored-by: Vadim Makeev <hi@pepelsbey.dev>

Author: dletorey

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

@@ -344,6 +344,20 @@ The {{cssxref("attr")}} CSS function now supports [`<attr-type>`](/en-US/docs/We
 | Beta              | 149           | No                  |
 | Release           | 149           | No                  |
 
+- `layout.css.attr.enabled`
+  - : Set to `true` to enable.
+
+### Namespaced attributes in `attr()` CSS function
+
+The {{cssxref("attr")}} CSS function now accepts [namespaced attributes](/en-US/docs/Web/CSS/Reference/Values/attr#namespaces). This allows you to take attributes from elements of [XML](/en-US/docs/Web/XML)-based languages, such as [SVG](/en-US/docs/Web/SVG) and style them accordingly. ([Firefox bug 2014060](https://bugzil.la/2014060))
+
+| Release channel   | Version added | Enabled by default? |
+| ----------------- | ------------- | ------------------- |
+| Nightly           | 150           | No                  |
+| Developer Edition | 150           | No                  |
+| Beta              | 150           | No                  |
+| Release           | 150           | No                  |
+
 - `layout.css.attr.enabled`
   - : Set to `true` to enable.
 

files/en-us/mozilla/firefox/releases/150/index.md

@@ -114,6 +114,10 @@ These features are shipping in Firefox 150 but are disabled by default.
 To experiment with them, search for the appropriate preference on the `about:config` page and set it to `true`.
 You can find more such features on the [Experimental features](/en-US/docs/Mozilla/Firefox/Experimental_features) page.
 
+- **Namespaced attributes in `attr()` CSS function**: `layout.css.attr.enabled`
+
+  The {{cssxref("attr")}} CSS function now accepts [namespaced attributes](/en-US/docs/Web/CSS/Reference/Values/attr#namespaces). This allows you to take attributes from elements of [XML](/en-US/docs/Web/XML)-based languages, such as [SVG](/en-US/docs/Web/SVG) and style them accordingly. ([Firefox bug 2014060](https://bugzil.la/2014060))
+
 - **Absolutely positioned elements in multi-column containers and when printing**: `layout.abspos.fragmentainer-aware-positioning.enabled`
 
   Absolutely positioned elements inside [multi-column containers](/en-US/docs/Web/CSS/Guides/Multicol_layout) and when printing are now correctly positioned and fragmented. This improves interoperability with other browsers and prevents layout issues such as overlapping text or content loss. ([Firefox bug 2018797](https://bugzil.la/2018797)).