I'm still on Firefox for a few reasons but I've been checking it out as it evolves, and been pleasantly surprised with progress over time.
There's a few things that I think are inherent to Chromium, that I doubt they'll ever get back; one of these is definitely MDI. But on the other hand, there's also a few things that I believed were Presto-specific (HTML renderer-related, e.g. text-selection of link text) that they have somehow managed to re-implement on top of Chromium, so never say never.
> Unfortunately, Vivaldi wasn't recreating that when I tried it.
Yeah, Vivaldi is not snappy. But... given the state of browser UI performance today (massively regressed from 8 years ago), it compares favourably to competitors. Which isn't to be sniffed at considering they've added so many things on top of the beast that is Chromium.
I'll give it another chance one of these days, though. I'm hearing a lot of news about it lately so I suppose there will be improvements and maybe the newer versions are closer to what I want.