In bug #206506, I had determined that we need to send a Firefox user agent quirk to accounts.youtube.com to avoid unsupported browser warnings on Google Docs. Either the user agent check has since become more aggressive, or it somehow depends on factors I don't understand, but as of today it's no longer enough. We now need the quirk for docs.google.com as well. For earlier history, see: bug #171941, bug #199153.
Created attachment 392588 [details] Patch
(In reply to Michael Catanzaro from comment #0) > Either the user agent check has since become more aggressive, > or it somehow depends on factors I don't understand I think my original quirk is only sufficient for Docs, not for Sheets or Slides.
Comment on attachment 392588 [details] Patch Clearing flags on attachment: 392588 Committed r257972: <https://trac.webkit.org/changeset/257972>
All reviewed patches have been landed. Closing bug.