While not being fully feature-complete (text-decoration and text-shadow are missing), CSS Highlight API can in its current state already be enabled on all channels.

Release Note Request (optional, but appreciated)
[Why is this notable]: Allows web developers to style ranges.
[Affects Firefox for Android]: yes
[Suggested wording]: Added support for the Custom Highlight API, which allows to style text ranges.
[Links (documentation, blog post, etc)]: https://developer.mozilla.org/en-US/docs/Web/API/CSS_Custom_Highlight_API

https://hg.mozilla.org/mozilla-central/rev/0a892fa7775c

Thanks, added to the Fx140 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 Fx140 release notes.

The priority property does not seem to be respected on CSS Highlight API
https://developer.mozilla.org/en-US/docs/Web/API/Highlight/priority

I have tested in:

• Chrome 136 - works as expected
• Safari 18.5 - works as expected
• Firefox Beta 140 - only respects the last highlight created
• Firefox Nightly 141 - only respects the last highlight created

This is my test CodePen - https://codepen.io/CodeRedDigital/pen/QwbbqoG?editors=1010

Hi Dave, thanks for your report. Let's move this to Bug 1968981.

The .add method of the CSS Highlight API can not be chained.
I have tried the following in the console:

const highlight = new Highlight();

const range1 = new Range();
const range2 = new Range();

highlight.add(range1).add(range2);

console.log(highlight.size); // 2

I have tested in:

• Chrome 136 - works as expected
• Safari 18.5 - works as expected
• Firefox Beta 140 - does not work
• Firefox Nightly 141 - does not work

Adding separately does work:

const highlight = new Highlight();

const range1 = new Range();
const range2 = new Range();

highlight.add(range1);
highlight.add(range2);

console.log(highlight.size); // 2

Please file separate issues for this and needinfo me on them, please. I've filed Bug 1969004.

(Really appreciate your efforts though, thank you!)

(In reply to Jan Jaeschke [:jjaschke] from comment #9)

Please file separate issues for this and needinfo me on them, please. I've filed Bug 1969004.

(Really appreciate your efforts though, thank you!)

Understood, thank you