Created attachment 125269 [details] The bug in action. SUMMARY Firefox, when having the "show title bar" option disabled, flickers when you press the maximize or unmaximize button. STEPS TO REPRODUCE 1. Use firefox with CSD. 2. Maximize or unmaximize it. OBSERVED RESULT The firefox window flickers and "changes size" mid-resize, to then go back to the normal size. EXPECTED RESULT Smooth maximize/unmaximize animation. SOFTWARE/OS VERSIONS Linux/KDE Plasma: 5.4.13-arch1-1 KDE Plasma Version: 5.17.90 KDE Frameworks Version: 5.66 Qt Version: 5.14 ADDITIONAL INFORMATION Scale method is set to Smooth, rendering backend is OpenGL 3.1.
As more info, this didn't happen (and doesn't happen) on 5.17.5 or earlier versions I'm able to test. I was able to reproduce this on KDE Neon Unstable.
Unfortunately KWin needs to resize Firefox and any other client-side decorated client twice when it gets maximized or restored. We have to do that because we don't know the extents of the client-side drop-shadow. I'm afraid it is CANTFIX on X11. There are several options available to you: - switch to wayland - disable maximize effect - don't use client-side decorations As for flickering, see bug 415839.