FEBE (Firefox Environment Backup Extension) is a free Firefox backup utility that functions as an add-on. You can have it do scheduled backups, backup your whole profile or pieces and parts (including other add-ons, cookies, etc.).
This is most helpful for me since I use NoScript to limit which scripts are allowed to run as well as Permit Cookie to determine which site cookies I want to retain after I close Firefox. Whenever I rebuild a laptop, it's handy to not have to manually install all add-ons, etc.
http://softwarebychuck.com/febe/febeFAQ.html