SUMMARY Crashing KWin, crashing compositing, using a fullscreen application that disables compositing, etc will make Firefox unusable and stuck at the last frame before the event. STEPS TO REPRODUCE 1. Open Firefox 2. Play a full screen video with mpv (which disables compositing) 3. Exit full screen 4. Go back to Firefox OBSERVED RESULT Firefox will be stuck on the last frame before disabling compositing and will not be interactive EXPECTED RESULT Firefox should be normally usable SOFTWARE/OS VERSIONS Linux/KDE Plasma: Fedora 34 KDE (available in About System) KDE Plasma Version: 5.22.80 KDE Frameworks Version: 5.85.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION I've tested this with both KWin 5.22.3 and git master and both on Arch and Fedora as well. This is on Xorg, using the amdgpu driver with a Ryzen 2500U APU that has Radeon Vega 8 integrated graphics.
Then that's a firefox bug
Reported on Mozilla's Bugzilla instance: https://bugzilla.mozilla.org/show_bug.cgi?id=1721841
Note that in Mozilla Ticket 1706934, [1] they want to refer this bug to KDE: > Do you mind to report it at KDE bugtracker? (https://bugs.kde.org/) I don't think we have manpower to work on it. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1706934#c3 (1706934 - Window content breaks for good with X11 EGL after suspending KWin compositing)