How to add Iceweasel file associations ?

[Tim Day <timday@bottlenose.demon.co.uk>]

After a successful upgrade to etch, I'm looking at the shiny new
Iceweasel 2.0.0.3.

If I 
  Edit->Preferences->Content->FileTypes-Manage
I see a list of extensions for various things (SWF, PDF, RA etc)
but how do I add new ones ?  There's buttons to change existing actions
or remove them, but none to add new ones.  What's the trick ?  Something
involving /etc/mime.types and /etc/mailcap instead ?

(Specifically, I want to get the .ram files linked from the BBC player's
"Launch in stand alone player" to actually launch realplayer rather than
just complaining there's no associated helper function for the filetype;
they work just fine if I download them and provide them to realplayer on
the command line, but it's a bit roundabout).

Thanks for any help
Tim