Thanks for this addon.
Feature wise, there's everything I need and it is evolving rapidly.

Unfortunately, I experience some bugs which make it a bit too unreliable atm :
- Sometime some "random" tabs groups are created (not by me). They did not come from new windows.
- When I switch from one group to another, some tabs switch to the new group (not all of them... just a few).
- Some tabs can't be moved to another group (with an error message explaining the operation is impossible)
- When switching to another group, sometime I get an error message warning that the current tabs will be closed. Don't know why but very annoying.

I can't confirm a 100%, but it seems these problems concern only tabs with URLs on my localhost or with local HTML files.
I should make more tests to confirm though.