As a part of my Google Summer of Code project, I am writing an extension to synchronize contacts from Google (tm) and an address book in Thunderbird. As a result, I know the basics of making an extension and have some familiarity with the code for Thunderbird (and the core of Firefox).
Below is a list of the extensions I have written. Click on the links for more details. If you have an idea for an extension use the Contact link above to let me know.