Yesterday, I submitted a new version of ThunderBirthDay to http://addons.mozilla.org, as promised recently. Its only change is that it now supports Thunderbird 5. It now usually takes a couple of weeks to get the new version approved, but you can already download it here:
If you experience any problems, or just want to let me know that it works, please drop a line here. Thank you!
Mozilla has just approved ThunderBirthDay 0.5.0. It is now downloadable via its official listing on addons.mozilla.org or via Thunderbird's extension manager, and will be updated automatically if it was already installed.