Rated 4 out of 5 stars
Makes it very easy to login to any sight, saves the time of manually typing everything in. Only thing that could make this better is password backup, in case you have to reinstall or refresh firefox for any reason, lost all my passwords twice now that way, I do keep a list of usernames/passwords for each sight I go to on a note pad on my scratch pad that I keep inside my computer.This review is for a previous version of the add-on (2.9.1-signed).
You might consider backing up the files in your profile folder. See https://support.mozilla.org/kb/profiles-where-firefox-stores-user-data
There's also Password Exporter https://addons.mozilla.org/addon/password-exporter/ which hasn't been updated in a long time, so it may or may not work.
I always figure, I didn't build the password manager, so I don't take responsibility for backing it up, especially when solutions already exist. But I hope you find those solutions helpful.