We're the only browser to produce cross-fade() values for mask-image. For compatibility reasons we should align with Firefox, Chrome and the spec (!) even though most other <image> properties use cross-fade() during animation (which is not what the spec dictates but is what Chrome does as well as WebKit).
Pull request: https://github.com/WebKit/WebKit/pull/10437
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/38670
Committed 260756@main (fd0581b4940c): <https://commits.webkit.org/260756@main> Reviewed commits have been landed. Closing PR #10437 and removing active labels.
<rdar://problem/105845275>