Great Add-on Rated 5 out of 5 stars
Please people, just read what this add-on does and don't complain about things it is not intended for.
If you have multiple instances of Thunderbird running (mostly on different computers) and you want to have the same address book on all these instances, then this add-on is just perfect for you. If you add an entry on one machine the most current version of your address book is stored (in a file, on IMAP, etc.) and downloaded on your other TB instances.
It's not for exporting your address book in various formats, or anything else - but that's just fine. It does what it says and it works perfect. Thanks for the effort!