Linux – Firefox: viewing text files in external editor

I would like to make Firefox view text files not in its internal editor, but in the external editor (namely EmacsClient).

Is it possible to change this default behavior of Firefox?

EDIT:
I beg your pardon for being inconcise, I'll try to state the matter once again. First thing to mention is that I use the Linux version of Firefox. That means that unlike the Windows version the contents of the application bindings dialog is very scarce.

When I click on the link to a text file (be it remote or local) by default Firefox opens it in the internal browser. I've tested, somehow it looks at file extension – when for example I make a file with .mpg extension, the behaviour is as it should be – the dialog with "Open With…" and stuff. When the file has unknown extension (unknown to /etc/mime.types), in my case it's .out, pure text format – the default behaviour is to open it in a Firefox window. That very thing I need to change.