The OpenPGP privacy extension for Thunderbird has been accepted as a Google Summer of Code (GSoC) project. Enigmail is looking for someone to help improve the UI. If you are interested, you can check out the Mozilla’s Summer of Code project list - Enigmail is at the bottom:
The mentor of this project is Patrick Brunschwig, so please send your application and list your top 3 pain points in the Enigmail UI, and what you would do to fix them.
The deadline is quick approaching (the 27th), so move quickly if you are interested! It’s a great opportunity to learn more about development, Thunderbird, and contributing to open source!