Project-Insanity

flatpak --user remote-add --no-gpg-verify firefox-wayland-git https://onny.project-insanity.org/files/firefox-wayland-git/repo
flatpak --user install firefox-wayland-git org.mozilla.firefox
flatpak --env GDK_BACKEND=wayland run org.mozilla.firefox

User dirs

rm -rf .flatpak_extras .local/share/flatpak

Debugging

flatpak --command=sh run org.mozilla.firefox
echo $XDG_RUNTIME_DIR

* Report bugs https://github.com/flatpak/flatpak/issues