Vivaldi is great on paper (if you don't care about it being F/OSS), but it's wildly unstable compared to all other major browsers including Firefox. Every time I try to use it as a primary, I end up running into something blocking within a week, reporting it, and switching back to whatever.

Which is a shame, because, stability aside, it really is the best option among Blink-based browsers, at least for the power user. No containers, sadly, but the problem there is Blink itself.