Rated 5 out of 5 stars

Fantastic :)
I now use this with Informational Tab - you get a little thumbnail. I did not realise that I needed an extra extension for that D'oh!
Small point: On 3.6 The tabs groups always open expanded when I start up Firefox :(
I have to click "Collapse All each time"

This review is for a previous version of the add-on (0.8.2009122501).