That sounds like tree style tabs except with colors, that you have to manually set groups instead of it being grouped based on what opened what, and it's still

That sounds like tree style tabs except with colors, that you have to manually set groups instead of it being grouped based on what opened what, and it's still horizontal so can't see more than a handful of tabs at the same time. On the other hand, it being native sounds like a big advantage (looking with one eye at xpi addons here, specifically the vertical tabs one Mozilla developed themselves and then immediately killed because it had been decided addons need to not be so powerful)