Changing the helpers for Firfox

[stan]

I did 2 installs of 5.10 this weekend. I downloaded and installed
Realplayer on both. The first, a test install, can open Realplyer stream
(from within Firfox) just fine. The 2nd (my laptop) tries to open these
with a Mplayer plugin, that doesn't seem to work.

How can I tell Firefox to use Realplyer, instead?

-- 
U.S. Encouraged by Vietnam Vote - Officials Cite 83% Turnout Despite Vietcong Terror 
- New York Times 9/3/1967