Thunderbird: definable external editor

It would be lovely to be able to define an external text editor for 
Thunderbird, and even better if the user is given access to all headers 
in the editor, as was done in the old console-mode newsreaders and mail 
user agents of yore (tin, trn, yarn, elm, pine-- among others). To 
understand why this would be useful, please note the line-wrap problems 
in my immediately preceding post, 'Automatic offline mode', which came 
of my attempt to reflow the last paragraph. Thanks,

Jeff