I've been using vivaldi-snapshot for a while now, because of the problems with ffmpeg, but I was always under the impression that it was a temporary workaround. After this morning's upgrade, I figured I should check it before deleting snapshot and firefox, so after a reboot I loaded vivaldi (stable) and tried to view a Formula 1 Practice 1 video. I'm glad I did.
Sadly, I just got a dead bird.
It's not such a burden to use the snapshot version for a while longer, but that version is far more likely to break from time to time than the stable version is. I'm hoping that maybe one more week is all that's needed, and by next Friday I'll be able to return to one browser to rule them all.