I have been getting several e-mails in this month wanting to know my suggestions and tips on what the best way is to backup your Firefox install.
FEBE (Firefox Environment Backup Extension)
Well my number one tip would be to use one extension that will make the job of backing up or syncing Firefox between two machines a lot easier. FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions and settings. It will actually rebuild your extensions individually into installable .xpi files. That makes synchronizing your office and home browsers a cake walk.
One more cool thing about FEBE is that it can preform on demand or scheduled backups for daily, weekly, or monthly unattended runs.
Google Browser Sync
Now if your using two computers on a day to day basis and you want to keep things in sync, a side effect of something like Google Browser Sync extension is that it keeps everything saved onto the other computer.
As long as you get your sync order straight – you could save your settings on your laptop Firefox install, then go back and reinstall Firefox on your desktop – put in the Google Browser Sync extension and everything should get moved back over as it was (as far as settings, bookmarks and cookies go). You’ll still need to reinstall your extensions however.
Backup by Hand (aka the hard way)
Last but not least, you could backup your Firefox by hand. What you want to do is make a copy of your Firefox profile folder. Depending on your operating system it might be in different locations.
Might want to check this page at MozillaZine for more information about where the profile folder is for your computer.