New Firefox Extension Packs All Your Extensions Into One .xpi File!
 

The Firefox Extension Backup Extension (FEBE) lets you backup all of your extensions, themes, bookmarks, preferences, and even cookies (you can pick and choose if you don't want to backup everything), while it's counterpart, CLEO (Compact Library Extension Organizer) bundles everything into a single .xpi file that you can install on any installation of Firefox.