Firefox Backup Extension is a free addon for Mozilla Firefox that allows you to backup and restore your complete Firefox browser Profile automatically. You can even perform regular automated and unattended scheduled backups of your Firefox Profile- daily, weekly, or monthly.

The backup of the profile includes the following:

- bookmarks/favorites
- cookies
- filled out forms
- extensions (It rebuilds your extensions individually into installable .xpi files)
- themes
- saved usernames and passwords

Download Links-

Windows version here
Mac version (Beta) here

Tip: To manually backup your Firefox profile, go to C:\Documents and Settings\Windows Porfile Name\Application Data\Mozilla\Firefox\Profiles. You will find a random lettered folder. Just select it and paste it somewhere else.