If all goes well this is a magnificent add-on. One can group tabs and easily switch between them. Very nice.

However when firefox or windows crashes the add-on sometimes cannot restore the groups. You end up with lots of tabs and one empty group. Restoring a backup (do make them) is not always working as expected. The tabs and groups are loaded but in a second firefox window. If this 2nd window is closed before the other firefox window you again lose all groups.

But even with this (big) problem I will keep using it.