Subject to FF bugs perhaps... Rated 5 out of 5 stars
So after some further reading, it appears that the issue might lie beyond this addon. Giving the benefit of the doubt, I've updated my rating back to 5 stars in the hope that the issue will be resolved and that it was unrelated to this addon. My original review remains below.
This piece of software has been very useful to me over the years and I would have given it five stars without hesitation, unfortunately it seems to be dying. Fundamentally it doesn't seem to be coping with the newer versions of Firefox (14/15 upwards). Seems to routinely die trying to save sessions and will frequently re-open sessions with some or all of the tabs erased (i.e. blank tabs). This later bug is disastrous for sessions that are autosaves.
I hope the developer can get this back to its once great status, but for now I cant recommend it. I'm going to try some other alternatives again like Tab Mix Plus or something and see if they are working more reliably.