Probably one of the best add-on I've come across! Rated 5 out of 5 stars

This repairs whatever reoccurring errors you may have experienced on Firefox, no matter if it's freezing or crashing. I'm a huge FF fan but a recent Window7 x64 update rendered it useless, so I had to switch to Chrome where their extension suck. Feeling desperate, I googled for a solution and this appeared on my search. I recommend this tool to EVERYONE!

Here's how to use it:

Is your Firefox freezing or crashing at regular intervals?
1. Install Places Maintenance add-on
2. Go to about:addons and open the add-on Options dialog
3. Select the Expire operation and click Execute
4. If you wish, uninstall the add-on (it's restartless, so the process is straight-forward)

Please check it out!

This review is for a previous version of the add-on (1.0.1-signed).