This is a must-have, life-saving add-on! Ever since TabMix Plus stopped working, I was looking for an add-on that would ensure that my tabs are restored when Firefox has a bad crash and can't restore itself.
But this add-on does so much more. It allows you to store your session manually or automatically. So whenever you notice that you are missing a tab (web page) from a few weeks ago, chances are good that you can find a backup.