Putting this here for folks just getting started with Thunderbird. Here are my most useful Thunderbird links that help me contribute every day.
Useful Thunderbird Links:
Thunderbird Build and Code Documentation - Tutorials on how to build Thunderbird from source, and how to create an extension. Also includes API and protocol documentation.
Thunderbird Blog - Thunderbird project blog, you can even add it as an RSS feed in Thunderbird itself (so meta)!
Connect - where ideas can be posted and voted. Also a gathering place for general discussion.
Thunderbird Website - You can download the stable and beta builds on the website.
Thunderbird Daily Build on Mozilla FTP - This is where you can go to grab the daily experimental development builds. If you head up a directory you can get other Thunderbird builds.
Thunderbird Support Website - You can ask support questions here, find information on how to use Thunderbird and troubleshoot problems. Itās a great resource if you are getting started or having issues with the application and need help.
Create a Thunderbird Bug - This link drops you straight into the Thunderbird product on Mozillaās Bugzilla. Here you can choose what part of the application you are having an issue with and report a bug.
Thundernest GitHub Page - Where the repository for the Thunderbird website lives.