Very good in the past. Rated 4 out of 5 stars
As of the latest Firefox release 15.0.1, Tab Mix Plus acted very weird. It disabled being able to open the Addons Window, it would no longer allow The Search Provider search function to work, and all favorites would no longer work, neither toolbar favorites or favorites in the Bookmark list.
Only option was to disable Tab Mix Plus in Safe mode and disable permanently there. Once that was done all functionality broken was restored.
Hopefully this can get fixed so this add on becomes usable again.
Other than the recent issue, this is a very good Add on.