Firefox ESR gives me "Already Running" error when opening new window


I seem to have a similar problem as mentioned in this post. Sadly there is no solution given.

I use Ubuntu 22.04 LTS Mate and changed from the default firefox snap to the esr/stable channel. The Ubuntu installation is “fresh” (no upgrade from previous), but has a few other things installed.

With firefox esr I get the following error whenever I try to open a new window via the firefox icon or command line and a firefox window is already open:

Firefox is already running, but is not responding. To use Firefox, you must first close the existing Firefox process, restart your device, or use a different profile.

The open window reacts normally, no problems there. I can drag a tab out to create a new window just fine. This happens on different user-accounts (probably all).

With the default version (latest/stable) a second window would open (like expected) - so it may have to to with differences in the esr version.

Is there anything I need to change in order to fix the problem? I would prefer to continue to use the ESR version as I configure ff via the policies file for multiple users, including options that are only available on ESR.

Additional info:
Session-Type: X11
firefox-snap-version: 115.2.1esr-1 (3130)
Output of env | egrep -i "session|moz":

SESSION_MANAGER=local/:@/tmp/.ICE-unix/2374,unix/:/tmp/.ICE-unix/2374 XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0

Whenever I start firefox esr via commandline I get this info - then firefox starts normally (first window) or gives the mentioned error:

Gtk-Message: 13:24:06.805: Failed to load module “appmenu-gtk-module”
Gtk-Message: 13:24:06.805: Not loading module “atk-bridge”: The functionality is provided by GTK natively. Please try to not load it.

I have not tested if I get the same info on the regular firefox version.