I tried Firefox 86.0 on ArchLinux with a KDE Plasma (Wayland) session. All Qt and GTK applications function normally. Firefox does not crash, but there is a noticable delay while typing or interacting with the mouse. It seems the input is received but it is not rendered on the screen. I used the profiler and [https://profiler.firefox.com/public/yzb8yhxcj918v1q2513prse3rq8x87wa61dvb88/stack-chart/?globalTrackOrder=0-1-2-3-4-5-6-7-8-9&localTrackOrderByPid=8446-5-0-1-2-3-4~8609-0~8818-0~&thread=0&v=5 uploaded a profiler session] to help you investigate the problem.