Intent to prototype and ship: content-visibility

[Frédéric Wang]

Summary: Add support for `content-visibility` property
Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1660384
Specification: https://drafts.csswg.org/css-contain/#content-visibility
Standards Body: CSS WG
Platform coverage: All
Preference: layout.css.content-visibility.enabled
Devtools bug: N/A

Other browsers:
  - Blink: Shipped since Chromium 85.
  - WebKit: Shipped in tech preview, implemented behind a flag.

web-platform-tests: Many tests are available in
https://wpt.fyi/results/css/css-contain/content-visibility ; a few
Gecko-only tests were introduced:
  - a11y tests:
browser_css_content_visibility.js/browser_treeupdate_csscontentvisibility.js
  - performance tests:
content-visibility-auto-relevancy-updates-stop-ticking.html,
test_dynamic_change_causing_reflow.html

See also
https://groups.google.com/a/mozilla.org/g/dev-platform/c/kVs-TVhreWQ/m/esjBny3NBQAJ
for a previous intent to prototype focusing on content-visibility: hidden.

As of 2024-01-22 I intend to turn intent on content-visibility by
default. It has been developed behind the
layout.css.content-visibility.enabled preference. Status in other
browsers is as described above.

Bug to turn on by default:
https://bugzilla.mozilla.org/show_bug.cgi?id=1874874

On bug 1874874 you can find an overview of the remaining WPT failures
and bugs, but the TL;DR is that the performance bug 1765615 is the only
one that seems serious enough.

Frédéric Wang

[Frédéric Wang]

Hello,

content-visibility has been disabled in beta 124 (but remains enabled in
nightly 125). This was decided due to a serious regression affecting a
common use case of pages combining content-visbility: auto and
contain-intrinsic-size. For details see
https://bugzilla.mozilla.org/show_bug.cgi?id=1880928