Firestorm fullscreen problem

[Jenya Juran]

Hi, I get the following error when I start Firestorm 7.1.11 on Windows11. See attached image.
I have enabled fullscreen in Preference:Graphics and Debug Settings.
At the same time the stock LL Viewer starts in fullscreen without problems.
Same happens with other resolutions like 1920x1080.
I am running out of ideas at the moment.

Any help is much appreciated and many thanks!