I have not digged deep into this bug, and I am not able to reproduce it, when it happen "I don't have time for it", so I just restart firefox, so I am not sure. But I had this bug only with firefox. But that doesn't say anything because firefox is one of the only GTK app I keep running for very long period of time.
I have only one issue, is that copy past is broken under wayland: https://bugzilla.mozilla.org/show_bug.cgi?id=1631061