Bug#885920: [firefox] Firefox window doesn't show under wayland

[Patrik Flykt]

> That explains it. Verified that Firefox works on GNOME/X11, enforcing
> GDK_BACKEND=x11 doesn't help either with wayland. Seems I need to
 > wait for newer Firefox versions and use X11 meanwhile.

With current Debian testing, there is no longer a problem. So some
(combination of) user space components contributed to the issues seen,
and Firefox works just fine now. Actually things started to work fine
some time ago, but I forgot about this bug report.