Hi, did you have any good fortune with this issue? I have similar problems on Fedora 40 and 1070 Nvidia GPU. Looks like Firefox is not affected, but the problem is also not present all the time in chrome based browsers, so maybe more time needed to confirm what’s going on with firefox.
I have tried Vivaldi and Thorium. Both seem to work fine without nvidia driver installed.
I switched over to libreworlf. Vivaldi is really feature rich, thorium is really snappy, but the flicker is major deal breaker. Some popup menus flicker so hard it’s almost like Christmas.
My guess is there is something wrong with hardware acceleration. I don’t know if on Chromium - Wayland it is enabled and it doesn’t work or it is not enabled but it is needed.
In Firefox you go on “help - more information” (sorry I don’t have it in English) and you are told about hardware decoding in “graphics”. In Fedora Firefox it should be enabled by default, given that you have installed drivers and codecs.
On a side note, Vivaldi is not a “browser” meaning it is a javascript (React?) GUI on top of Chromium, Chromium is Chrome minus some features from Google. Thorium is Chromium with some tweaks, Librewolf is Firefox with some tweaks. In short you are just picking different “mods” of Chromium and Firefox.