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:
MDN Thunderbird 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)!
Thunderbird Wiki - Has a lot of useful community information here. If you want to know who takes care of what, this is a good place to look it up.
Thundernest GitHub Page - Where the Thunderbird website repository lives, more projects will likely live here in the future. For now this is where you go to contribute to the TB website project.
Thunderbird Website - We’re in the process of moving to our new website, Thunderbird.net - the old website was at Mozilla.org. Since we are focusing on taking Thunderbird in its own, unique direction - it has its own domain name now. You can download the stable and beta builds on the website.
Thunderbird Nightly Build on Mozilla FTP - This is where you can go to grab the Nightly, if you head up a directory you can get other Thunderbird builds.
Create a Thunderbird Bug - This link drops you straight into the Thunderbird product on Mozilla’s Bugzilla. Here you can choose what part of the application you are having an issue with and report a bug.
Thunderbird on Mozilla Support Website - You can ask support questions here, find information on how to use Thunderbird and troubleshoot problems. It’s a great resource if you are getting started or having issues with the application and need help.
This Forum! - Including this in the event that someone has copied and pasted these somewhere. The forum this is posted on is a great place to share information, ideas, and talk about Thunderbird!