Rated 2 out of 5 stars

It won't work on thunderbird 11.x.
But the idea is very good.
I feel one big drawback of this addon is the keybind, which is not populer one such as emacs like or gmail like.

For example, I am emacs user so I use Firemacs on Firefox.
If I were you, I would rename to "Thundermacs" (if the firemacs owner agreed,)
and default keybind should be more emacs like one.