A lifesaver Rated 5 out of 5 stars
My gratefulness for this extension grows with every new Firefox version that is released and is even more unstable and freeze-happy than its predecessors. I am using Firefox 14 on all of my systems now (Win7/OSX/Ubuntu), and it isn't jolly how often it will just flat-out freeze, never to recover, during regular use. And you can bet that this is going to happen after you've spent 20 minutes typing out that intricate, insightful, page-long response to some discussion thread. Drat!
Take my advice and install Lazarus, if you haven't already. The best thing about it is that as long as everything works fine, you don't even notice it's there. But next time you lose many minutes of work because of Firefox crashing or some other problem, you'll remember it. And your input is restored in a few seconds. If you're concerned about data protection, it has facilities to not store number fields (i.e. credit card information), and you can opt to encrypt the whole database.
"Lifesaver" might be a hyperbole in most cases. But Lazarus is definitely a timesaver, and it's good at its job. The nerves this thing has spared me, it probably added a couple of months to my lifespan by now.