SUMMARY ...creating a black border on top and left side of the desktop ~30px wide. After FF finishes starting everything returns back to normal. SOFTWARE/OS VERSIONS KDE Plasma Version: 5.18.90 KDE Frameworks Version: 5.70 Qt Version: 5.15.0 ADDITIONAL INFORMATION Might be a Kwin issue or may belong somewhere else.
Also opening a new window if FF is already running has the same result.
Can you create a video? Also confirm if it happens without compositing (alt + shift + f12)
Created attachment 129149 [details] Video recording of the bug The bug doesn't occur without compositing. I also use "GTK_USE_PORTAL=1", "MOZ_ENABLE_WAYLAND=1" and "MOZ_USE_XINPUT2=1"
Those environment variables have no effect on this issue. FF Nightly and Thunderbird also cause this issue. All three only do this if CSDs are enabled. I previously said: "...desktop content briefly shifts...", but if there are already windows of other apps on the desktop they also move. Or maybe it's not app widows that move but rather the area that shows windows shifts up and to the left because FF tries to open outside of it?
Bizarre. Cannot reproduce. This is with Wayland? Or X11?
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It was originally on Wayland but I can't reproduce anymore.