Difference between Thunderbird and Firefox add-ons

I created a simple Firefox addon with an Add-on-SDK that changes the config value: https://github.com/rubo77/devPixelsPerPx-Toggle

This addon works great on Firefox, but I would like it to work for Thunderbird as well.

What's the difference between the firefox add-on and the Thunderbird add-on?

Or do I need to use a different SDK when I want to develop a Thunderbird add-on?