I googled around and found a great wikipedia article on text editors - http://en.wikipedia.org/wiki/Wikipedia:Text_editor_support
I installed Mozex which is something that will let you run external commands for certain Firefox things. I configured it to run emacs when I edit in a text area.
Mozex configuration to run emacs as an editor:

Mozex in use:

I also followed instructions on installing Emacs Wikipedia Mode which provides syntax highlighting and edit commands appropriate for wikis.
So far everything is working nicely. I have the same set-up on the Mac and on the Linux desktop.