I remember around 2012 Firefox did use to have tab grouping, and they dropped the functionality after. I remember a friend of mine being annoyed for that, although I myself didn't appreciate much the functionality.
Oh, it's better than that: They had tab grouping as a native feature, and it was great, then they factored it out into an extension... and then they changed the way extensions worked, and didn't bother porting it. Kind of an insulting way to kill a feature IMO.