Use Sidebery in Firefox for vertical tabs and it has not only better grouping but also entire "tab spaces" (workspaces) which you can switch between as well, if wanted.
>>ddooli+is
I've been trying Sidebery since about 2 minutes after I made my last comment, and I think I like Sidebery more--and I've been using Tree Style Tab for _years_
Sidebery responds noticeably faster, and the panels are a great feature.