Thunderbird makes it unnecessarily hard in the default configuration to send inlined patches, as it makes it hard to unset format=flowed.

This extension was meant to help, by providing a menu item "Send Patches..." in the "File" menu.

However, Marius improved it, and wants to improve it even more, adding tighter integration with Git, so that renaming it to "ThunderGit" seemed appropriate. Therefore, you should look at ThunderGit instead of this project.