Right... I use multiple browser windows as tab groups. Tried tree tabs, but since I keep one window per topic I rarely get enough tabs open to need them.
I'm still confused why people are so hell bent on using a single window exclusively. It's a natural way to group the tabs and it was there from day one!
Especially since modern desktop environments will have a gesture or something to give you a preview of all your open windows. What's annoying is that they all seem to shuffle the spatial order of the window previews whenever they feel like it.
I tried that, but eventually they just all blended so that now I've got three different windows with 50 of the same tabs open. Groups can have labels so that I can see which group is which.