Summary

That is enable layout.css.content-visibility.enabled

I'm providing details of Igalia's analysis below, but the TL;DR conclusion of talking with Mozilla folks is that only bug 1765615 is a blocker. Hopefully the main patch to fix that bug will land soon.

I'm proposing next Monday as a target date, so that it happens after the soft code freeze for Firefox 123 ( https://groups.google.com/a/mozilla.org/g/dev-platform/c/X7zK5k7-LOE ), and we have time to finish bug 1765615 and address other minor issues.

Details

• Intermittent failures:

  • content-visibility-auto-state-changed-first-observation.html => recent bot reports (2024-01-09), reproducible locally.
  • content-visibility-030.html => recent bot report (2024-01-14), not reproducible locally.
  • content-visibility-animation-in-auto-subtree.html => recent bot report (2024-01-06).
  • content-visibility-with-top-layer-005.html marked as flaky on all platforms.
  • content-visibility-with-popover-top-layer-005.html marked as flaky on all platforms.

• WPT failures:

  • content-visibility-with-top-layer-in-auto-subtree-removal.html => this passes, but has a max-assert: 2. The assertion: "Out-of-flow frame got reflowed before its placeholder" is a known bug which is not related to c-v, see https://bugzilla.mozilla.org/show_bug.cgi?id=1828898 and https://bugzilla.mozilla.org/show_bug.cgi?id=1863402
  • content-visibility-095.html => a rendering bug with full effect of contain: layout not applied to content-visibility: hidden.
  • content-visibility-size-containment-001.html => a minor existing invalidation bug for size containment when switching relevancy of content-visibility auto elements. present in other browsers too.

• WPT failures due to feature we don't implement (won't block shipping content-visibility)

  • content-visibility-animation-with-scroll-timeline-in-auto-subtree.html and content-visibility-animation-with-scroll-timeline-in-hidden-subtree.html:
    • These depend on CSS scroll-driven animations, which is currently disabled by default
  • css/css-view-transitions/ [3d-transform-incoming.html, content-visibility-auto-shared-element.html, css-tags-paint-order-with-entry.html, and 39 others
    • view transitions isn't supported
  • content-visibility-048.html and content-visibility-auto-text-fragment.html
    • url-scroll-to-text-fragment isn't supported
  • content-visibility-080.html
    • caretRangeFromPoint is not supported, https://caniuse.com/?search=caretRangeFromPoint
  • content-visibility-svg-path.html
    • checkIntersection, checkEnclosure, getIntersectionList and getEnclosureList, these svg functions are not supported

• Bugs with proposed enhancements (won't block shipping content-visibility)

  • Update details/summary to use "content-visibility:hidden" for hiding
    • This is a proposal to make the implementation of these elements rely on content-visibility. It cannot be done until we ship content-visibility, but shouldn't be a prerequisite to ship it.
  • [css-contain-2] filter effects and "relevant to the user" (for content-visibility:auto)
    • This is a proposal to refine when a content-visibility:auto element becomes relevant, by taking into account possible filter effects. There is no WPT test for that and the added text is quite generic, probably shouldn't be a blocker?

Intent-to-ship: sent but didn't show up on dev-platform yet

https://hg.mozilla.org/mozilla-central/rev/75c3c3ed6fe2

Related PR

• Firefox Release note