I wonder if Youtube doesn't run CI tests against other browsers than Chrome or if those test cases just aren't covered. According to an analysis in the Firefox bugtracker ( https://bugzilla.mozilla.org/show_bug.cgi?id=1697551 ) it seems like the error occured because a non-standard attribute is used in the JS code that only Chromium implements. Looks like the changes are being rolled back though. Geniunely happy to s…
They have a strong financial incentive to break functionality in browsers that aren't theirs. Why would they ever care to test?