I was sad, too
There are probably not many of us still/ever using this.
I extracted the XPI and while i'm not quite sure what's going on, it's related to the nsIPref*() calls, i believe here:
../chrome/content/exteditor.js: prefNotifierExe = nsPreferences.copyUnicharPref('exteditor.default.editor', "");
(Ha, documentation for this is pathetic, but it seems this changed when "nsIPref" was replaced by "nsIPrefBranch". Also, i presume that nsPreferences is inherited by thunderbird extensions, because i don't see it being assigned in the XPI anywhere, only referenced.)
I tried changing that to '.getCharPref(...)' to no avail.
So, right now, i have a hardcode to the script i use to perform edits via gvim :
// SDOWDY HARDCODED
extEditorRunProgram(prefNotifierExe, params, editorObserver); // non blocking call
IT WORKS FOR ME(TM) for now, but i'm not thrilled with it. If i figure it out (i'm a sysadmin, not a mozilla developer...) , i'll try to post back.