Vivaldi is about to drop support for Manifest V2 as well:

https://www.reddit.com/r/vivaldibrowser/comments/1urieed/com...

I'd been using it solely for GMail / Google Drive / etc. at work, for whatever improved compatibility a Chromium browser might provide over Firefox, which I use for everything else. I got the warning that UBlock Origin won't work, and I immediately ditched Vivaldi. I'm sad about it, I think Vivaldi otherwise is a good browser.

I love Vivaldi, but it also uses Chromium. If an extension is not in the Chrome Web store Vivaldi will not be able to install it.

Firefox seems to be the only reasonably mainstream option for proper ad blocking.