kiosk mode fails to start on Ubuntu 25.10 Firefox

[teledyn]

This would be using the default Firefox snap install from the Ubuntu 25.10 distro, the script installs the policies but when I quit FF and restart with the -kiosk switch, I get a black screen and nothing further, run from the command line there are no further messages after "not loading atk-bridge" which is already provided by GTK.

Looking at the policies listed, I can't see any of them impacting only the -kiosk mode, but I also know very little about FF configuration. Could there be a policy that now needs to be added?

[zeitisen]

I have the same problem. But its not a snap problem. I have an installation with firefox 147.0.1 from https://ppa.launchpadcontent.net/mozillateam/ppa/ubuntu/ , because I have other problems with firefox from snap.
With firefox from ppa it is the same problem.

[zeitisen]

I just made a few tests. It works, if there is already a firefox window.
If you then use
firefox -kiosk wikipedia.org
the window is opened in the existing firefox.
If you use
firefox --private-window --kiosk wikipedia.org
then you get a Kiosk window. The reason for this is not clear.
The option --kiosk-monitor did not help in any way.

[zeitisen]

I tested this on Ubuntu 25.04 with the same firefox version. There it works as expected. So it is a problem with gnome 49

[teledyn]

I had found changing MOZ_ENABLE_WAYLAND to zero, despite my running Wayland, kiosk now works. That it always worked before may also be explained by a gnome update and I only noticed when I restarted to test the policies.

[zeitisen]

If you do this you are working with xwayland which may be slower.
I also tried to use the switch --kiosk-monitor , but was not successful because i used an ordinary number 0 or1 or 2.
Now I read in other forums, that this may be a hex number like 0x1234. The number can be retrieved with
hwinfo --monitor and works independant of xserver or wayland. See here.
I haven't tested this yet.