We've had the container style queries pref enabled on Nightly since v149 (bug 2014404), while working on making the implementation more complete. I think we're at a point now where it would be reasonable to enable the feature for all channels, and let it ride the train to release.

On the interop-2026 subset of tests, we are currently showing 97.2% on wpt.fyi, which is a slightly higher pass rate than any of the other browsers. The only outstanding issues there are a test that involves CSS attr() (not yet enabled by default, but will pass when we pref on that feature), and an invalidation-related test involving rem units (see bug 2024049).

There are additional issues related to invalidation (e.g. bug 2028142), but other browsers also fail to handle this (along with other cases such as re-matching during animations), so I don't think this should block an initial "MVP" release.

https://hg.mozilla.org/mozilla-central/rev/3d33ef274c71

[Why is this notable]: New CSS feature
[Affects Firefox for Android]: yes
[Suggested wording]: Container style queries are now supported allowing to apply styles to an element based on the computed values of custom properties of their container. This can be done by using one or more style() functions inside @container rules.
[Links (documentation, blog post, etc)]:
https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Containment/Container_size_and_style_queries
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@container#container_style_queries

Thanks, added to the Fx151 nightly release notes, please allow 30 minutes for the site to update.
Keeping the relnote-firefox flag as ? to keep it on the radar for inclusion in the final Fx151 release notes.

Related Pull Requests

• Content PR
• BCD PR
• FF Release PR