TEBE (Thunderbird Environment Backup Extension) allows you to quickly and easily backup your Thunderbird extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files.
TEBE backs up and restores your extensions, themes, and (optionally) your address books, message folders, preferences, and more.
Backup as little or as much of your Thunderbird environment as you wish. Perform backups on demand or schedule daily, weekly, or monthly unattended runs. Sequential backups can be stored in timestamped directories so you can restore back as far as you like. Offers Box.net integration to store your backup online. More Info »
TEBE is from the maker of FEBE - Firefox Environment Backup Extension
(TEBE is currently in beta development but is fully functional.)