Rated 5 out of 5 stars

Thanks, This addon is great on the few birthday's I've tested. Is it possible to get it working with Cardbook address lists? I've started using Cardbook and am no longer maintaining Thunderbird's default address books. Cardbook is CardDAV compliant and they are trying to have it become the default address book for Thunderbird.

This review is for a previous version of the add-on (1.0). 

CardBook has its own birthday calendar feature, that uses different, incompatible concepts. I'd suggest to use that if you use CardBook for contacts.

Also, CardBook does not interface with Thunderbird's add-on APIs and is thus inaccessible for other add-ons like this one ;)