My Mac let's me use emacs keyboard shortcuts everywhere. I'm really sad that I don't get that in Linux. How the universe ever got into this state is beyond my comprehension. Mail.App has gotten me hooked on emacs keybindings when typing emails especially.
The solution in Linux, it turns out, is to just use emacs. I already have It's All Text for Firefox, with emacsclient as the editor. I just found External Editor for Thunderbird, with emacsclient as the editor and tbemail-mode for extra goodness. I think that'll do.