A colleague of mine tried Vivaldi 1.5 years ago, while he liked the split screen feature he found it way too slow and it had serious lagging issues from time to time. Much can happen in 1.5 years and I don't know if they were using V8 back then. But yeah, what I saw wasn't really that impressive. And no open source? Yeah, I think I'll stick with Firefox and my tinfoil hat extensions a while longer.