To be fair, I am on the beta upgrade channel and I'm using the same portable install from like 10 years ago.
Yes, it's Firefox. The black screens are a known problem, I think it has to do with hardware acceleration. They seem to have stopped in the last beta though, now the session manager sometimes can't restore session when I shutdown without closing FF first, it sees the session, it shows it as a list, I can open the tabs back one by one but it can't do it automatically for some reason.
And they forced their CEO to resign because fascism. Right around that time Firefox OS died.
Oh well, you can't not use Firefox, Chrome is the agent of evil and Edge is the dumb child of the former agent of evil.