I run Opera GX. But I think the performance issues are a lot more on my end. The browser sometimes gets visual glitches even when rendering normal pages (I get white squares that hide sections of the screen). It isn't related to your game, it's just something I have to deal with from time to time.
I also tend to run like a million open tabs at the same time, so perhaps that has to do with the visual glitches (maybe the browser runs out of memory or something).
That's why I'm thinking of running it on Edge, as a single tab, so that all of my machine's resources can be focused on that.