helper applications in firefox 3

[Pierre Frenkiel]

hi everybody,
I fought a while against this marvelous firefox 3, trying to convince it
to play ra files from a web site, but it won the 1st battle. I hope the 2nd one will
be for me, with your help.

First, I had this error message:
      xxx.asp could not be opened because the associated helper application
      does not exist. change the application in your preferences.
Not very helpful, as they dare not tell the name of this missing
application. Anyway, I tried to modify edit/preferences/applications,
putting realplay as application for the 2 RA file types there, but I
still got the same error.

Then, I found in prefs.js a line(God knows where it comes from):
   user_pref("plugin.disable_full_page_plugin_for_types", .....audio/x-pn-realaudio......

I removed this line, and now firefox opened the mplayer plugin for
the ra files, played it a couple a time, but after the 3rd try, it
  stops  just after connecting.

After that, I discovered that on my laptop, with the same URL, it opens
realplay which works perfectly. The only difference I knew was that
mozplugger was installed on my laptop. So, I installed it on the
desktop, and I have now 2 identical installs, as far as I know (same firefox, same 
mozplugger, same .mozill tree)... and firefox still opens the
mplayer plugin instead of realplayer.

Can anybody explain that? There is obviously  other differences, but
I'm unable to find them.

-- 
Pierre Frenkiel