Intent to implement & ship: CSS container style queries

[Jonathan Kew]

As of Firefox 151, I intend to turn CSS Container Style Queries on by default for all platforms.

It has been developed behind the layout.css.style-queries.enabled preference.

Status in other browsers is as shown below.

Bug to turn on by default:
https://bugzilla.mozilla.org/show_bug.cgi?id=2030645

Summary:
Style queries (a part of CSS Container Queries) provide a way for stylesheets to query the current styling of a container element, and conditionally apply additional CSS to the contents of that container.

Bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=1795622

Specification:
https://drafts.csswg.org/css-conditional-5/#container-rule

Standards Body:
CSSWG

Platform Coverage:
All

Preference:
layout.css.style-queries.enabled

DevTools Bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=2002239

Extensions Bug:
n/a

Use Counter:
n/a - included in interop-2026 suite so will be widely exposed

Standards-Positions Discussion:
https://github.com/mozilla/standards-positions/issues/686 [positive]

Other Browsers:
- Blink: shipped since Chrome 111
- WebKit: shipped since Safari 18.0

web-platform-tests:
https://wpt.fyi/results/css/css-conditional/container-queries?label=master&label=experimental&aligned&q=style