Look at CLEO and FEBE.
FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files. Now you can easily synchronize your office and home browsers.
CLEO (Compact Library Extension Organizer) is a Firefox extension that works with FEBE to package any number of extensions/themes into a single, installable .xpi file.
also, OPIE (Ordered Preference Import/Export) is a Firefox extension that allows you to import and export your installed extension preferences. This is useful when installing extensions in a new profile, or synchronizing multiple Firefox installations.
I also keep my profile backed up for recovery and to start using it on a new machine.