Rated 3 out of 5 stars
First of all, let me say that this was a great addon which I used pretty much on all Firefox installations.
It has many features that aren't available in any other addons even today, such as importing / exporting / suspending or hibernating individual tab groups.
Sadly, starting from Firefox 20, the continuous updates of the browser broke compatibility with this addon.
The fact that addon was never updated past 2011 doesn't help either.
Right now it simply has too much bugs and too unreliable to use, up to the point of loosing all suspended tab groups after restarting a browser, or crashing the browser entirely. Plus, it doesn't use the native group management of Firefox,
using its own system instead, so any other Tab Group enhancing addons are incompatible with this one.