Revert https://hg.mozilla.org/mozilla-central/rev/fc4ad3fce1b7 to ship MOZ_ENABLE_WAYLAND for Flatpak on Wayland.

Since bug 1720497, Firefox is able to start on Wayland even without MOZ_ENABLE_WAYLAND=1 env var if no Xwayland DISPLAY env var is found.

$ LANG=C flatpak run org.mozilla.firefox about:support

Window Protocol xwayland

$ env --unset=DISPLAY LANG=C flatpak run org.mozilla.firefox about:support

Window Protocol wayland

Verified:
VP8 VAAPI (on older Intel Iris Graphics 6100 (BDW GT3)), getUserMedia audio, screensharing, file download, file upload and opening external app (by opening mailto:info@example.com) work for me.
H264 VAAPI works after $ flatpak install org.freedesktop.Platform.ffmpeg-full/x86_64/22.08

This change was partially reverted by restoring --socket=wayland.

Restoring --socket=fallback-x11 would make flatpak behavior inconsistent with other platforms: when both x11 and wayland are available then currently ff chooses x11 unless forced with MOZ_ENABLE_WAYLAND. With --socket=fallback-x11 it would always choose wayland instead.

This only makes sense when wayland becomes default ff backend on all platforms.

(In reply to Emerson Bernier from comment #1)

With --socket=fallback-x11 it would always choose wayland instead.

Yes, and bug 1836342 for Snap.

This only makes sense when wayland becomes default ff backend on all platforms.

IIUC, Wayland can only become the default backend for packaged variants of Firefox that have a correct .desktop file, otherwise Firefox wouldn't have an icon.
All users of the Firefox/Thunderbird binary need to be migrated to Mozilla's Debian package (bug 1799516, bug 1751153 comment 45), Flatpak (bug 1278719) or Snap (bug 1665641).