I'd skip the context sensitivity part. The browser is not a high grade AI that knows what you're doing nor should it attempt to be one.

you mean the different "spaces" in the video for work, thesis, etc.? i don't think that's AI driven, it looks like the user manually puts a tab into a space and tabs open in the current space by default.

That's pretty much what I initially thought/hoped Firefox 'containers' were. But it's not, with those you can have X open tabs in Y different containers all in the same window.

Wow, this is a cool concept. Efficient tab management especially is a feature that should be baked into browsers, there should be no need to install an extension for that.