Some time ago, I reported through bugzilla (@seb128 told me to do so) against Firefox: when I open a private window when a normal window is already open, I get a choppy behaviour of both Firefoxes.
Well, I think the issue is wider because I experience it too running the Chromium snap.
This bad behaviour is not always noticeable, though. I do use a GNOME Wayland session, Ubuntu 20.04 with all up-to-date.
Does anybody see the same bug?