- using hardware accelerated video decoding is bizarre if the video uses VP9 (even disabling it or forcing AV1) it stutters from time to time;
- watching a video in the background and playing game at the same time, with hybrid graphics, freezes/hangs kWin, then, the video that was playing in the browser becomes green and everything that used either iGPU or dGPU starts to struggle and stutters a lot, forcing me to log in and out, i. e. restart my session manually;
The last one may be because of Nvidia (yes, my fault for having this card) prime offload in Wayland, but even so, I did not find any topic related to this, that has not otherwise been solved in bugzilla, and honestly I am kind of afraid to report this and be met with judging questions; I'd like to debug some more, but I don't have the patience.
These are the two ever lasting headaches that I have with Firefox. None of this bothers me enough to leave Firefox though.
Anyway, my congratulations to the team. Today, I have successfully converted 5 people to use Firefox.