One of the best tools I have found thus far for backing up your settings and profile in Firefox is MozBackup. I have tried them all, and this freeware program is the one I keep coming back to.
MozBackup is a simple utility for creating backups of Mozilla Firefox, Mozilla Thunderbird, SeaMonkey, Mozilla Suite and Netscape profiles.
It seems like some other backup programs for Firefox miss something, or don’t restore just right. MozBackup does just about everything right, and hasn’t done me wrong yet.