how to make Firefox use a program on a particular extension

[Claude Jones]

I've got Kaffeine running on top of mplayer with the WM codecs to play .wmv 
video files. BUT, every time I click on one from within Firefox, it pops up a 
dialogue asking if I want to use Totem. In Firefox's download preferences 
tab, in the 'file types' window, there's an entry for Microsoft WMV video and 
it says to use Kaffeine. There's a difference between this and the row above 
which has three columns; it looks like this:

RAM	RAM file 		Open with realplay
	Microsoft WMV video	Open with Kaffeine

It seems like this could be the issue, but I don't know how to fix it. I've 
also gone into KDE Control Center and configured file types there to use 
Kaffeine for .wmv, and from Konqueror, this works. 

Any ideas? 
-- 
Claude Jones
Bluemont, VA, USA