Probably related to #107 as well. If I force the wayland backend by running from the terminal GDK_BACKEND=wayland flatpak run org.mozilla.FirefoxNightly it does use a Wayland session.
Yes, thant's correct. Mozilla is going to produce Wayland enabled builds and the X11 backend has to be the default one. Jan is going to fix that on flatpak side.
Nightly version 20181108022619 runs in xwayland mode instead of Wayland. I think it's related to https://bugzilla.mozilla.org/show_bug.cgi?id=1503592 (Make X11 Gtk backend default).
Probably related to #107 as well. If I force the wayland backend by running from the terminal
GDK_BACKEND=wayland flatpak run org.mozilla.FirefoxNightly
it does use a Wayland session.