The extension withExEditor[1] can open the editor of your choice in its own window, optionally with a different editor config file. Your editor writes to a file in /tmp and on each write, the text in the input field or area in your browser is updated with the contents of the file. This is an advantage over Tridactyl, by the way, since in Tridactyl you have to close the editor in order to update the text inside the browser.
[1]: https://github.com/asamuzaK/withExEditor