Disclaimer: I've basically never used roll20 because it's way too heavyweight for my games; I use Owlbear Rodeo instead. But I have tech-savvy DM friends who use and like Foundry
I use Foundry VTT regularly (and develop a plugin for it). While I've never had functionality problems with Firefox, in practice, it's the main thing I keep a Chromium install around for, since on heavy scenes even Chromium barely holds up the frame rate on my laptop, and Firefox is notably worse. This is running on integrated graphics though, it's possible Firefox is fine with a more gaming-friendly setup.
Both of those look quite interesting for my usecases (In person/occasional hybrid games with a vtt/online only - depends on my groups current location and schedule)
Disclaimer: I've basically never used roll20 because it's way too heavyweight for my games; I use Owlbear Rodeo instead. But I have tech-savvy DM friends who use and like Foundry