It actually creates individual installable .xpi (or .jar for themes) files that you can put on CD, Flash Drive or floppy (do they still make those?) and install on another computer. You could also backup your extensions before installing an extension upgrade.
This way you could always go back if the upgrade doesn’t work for you. You may have a really good (but old) extension installed that is no longer supported and you don’t want to loose it. Now you can snatch it out of the bowels of Firefox and keep it archived. The latest version will (optionally) backup/restore your bookmarks, preferences, cookies and just about everything else that Firefox generates. You can even backup/restore an entire profile in one step.
Backups can be performed on demand or scheduled for daily, weekly, or monthly unattended runs.
A comprehensive debug mode allows for troubleshooting complex platforms.
Version 4.0 supports Windows XP and Linux/Unix.