I think I've found it. https://bugs.launchpad.net/ubuntu/+source/firefox/87.0+build3-0ubuntu2 introduced "MOZ_ENABLE_WAYLAND=1" in the startup script (/usr/bin/firefox). This was to fix #1916469, but unfortunately this breaks WebGL on Xorg. Removing "export MOZ_ENABLE_WAYLAND=1" fixes the problem.
As an aside, Firefox 88 should behave better in that regard (https://bugzilla.mozilla.org/show_bug.cgi?id=1695453 improved handling of setting MOZ_ENABLE_WAYLAN) ** Bug watch added: Mozilla Bugzilla #1695453 https://bugzilla.mozilla.org/show_bug.cgi?id=1695453 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1923116 Title: Broken WebGL in Firefox 87.0 on Kubuntu 21.04 Beta (Xorg) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1923116/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
