This WPT is failing because preventDefault on mousedown prevents proper handling of mouse events in iframes, as can be seen in this test case: https://mustaqahmed.github.io/web/interop/cancel-mousedown-in-iframe-top.html
<rdar://problem/116516596>
Pull request: https://github.com/WebKit/WebKit/pull/18685
Committed 269246@main (e837c341a756): <https://commits.webkit.org/269246@main> Reviewed commits have been landed. Closing PR #18685 and removing active labels.