This should be mentioned in the Nightly release notes. Keith, could you please make a relnote request?

Sebastian

Release Note Request (optional, but appreciated)
[Why is this notable]: Enable Scoped Custom Element Registries in Nightly
[Affects Firefox for Android]: Yes
[Suggested wording]: Enable Scoped Custom Element Registries in Nightly
[Links (documentation, blog post, etc)]: https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry/CustomElementRegistry

Reverted this because it was causing devtools failures in browser_webconsole_object_inspector_entries.js.

• Revert link
• Push with failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | devtools/client/webconsole/test/browser/browser_webconsole_object_inspector_entries.js | DEVTOOLS GENERATED-TEST FAILURE! SEE: https://firefox-source-docs.mozilla.org/devtools/tests/js-object-tests.html

L.E. Please also check these wpt failures and these ones.

(In reply to Keith Cirkel [:keithamus] from comment #2)

[Suggested wording]: Enable Scoped Custom Element Registries in Nightly

I think the wording can be improved a bit. Maybe something like this (borrowing from the Interop 2026 description of that feature):

Starting with Firefox 156, Firefox Nightly supports Scoped Custom Element Registries. Those registries can be created using the CustomElementRegistry() constructor that are separate from the global window.customElements registry. Creating more than one registry is useful for multiple custom elements that have the same tag name to coexist.

Sebastian

(In reply to Sebastian Zartner [:sebo] from comment #7)

(In reply to Keith Cirkel [:keithamus] from comment #2)

[Suggested wording]: Enable Scoped Custom Element Registries in Nightly

I think the wording can be improved a bit. Maybe something like this (borrowing from the Interop 2026 description of that feature):

Starting with Firefox 156, Firefox Nightly supports Scoped Custom Element Registries. Those registries can be created using the CustomElementRegistry() constructor that are separate from the global window.customElements registry. Creating more than one registry is useful for multiple custom elements that have the same tag name to coexist.

Sebastian

Thanks Sebastian, that wording is much better.

Backed out for causing unexpected ok wpt failures at sanitizer-custom-elements-constructor.html
Backout link
Push with failures
Failure log(s)
Failure line: TEST-UNEXPECTED-OK | /sanitizer-api/sanitizer-custom-elements-constructor.html | expected ERROR

https://hg.mozilla.org/mozilla-central/rev/b6e83b8a54d3

Thanks, added to the Fx156 nightly release notes, please allow 30 minutes for the site to update.
The nightly-only note will be removed after three cycles or when it is enabled by default, whichever comes earlier.

FF156 MDN docs work for this can be tracked in https://github.com/mdn/content/issues/45434

FYI Donal, a better link for docs is probably https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_custom_elements#scoped_custom_element_registries - added a request for info, but that's just so you get notified of this.

Release note updated