firefox should use gnome/nautilus defaults/options for opening files

Open firefox
Browse somewhere
open some file, in my case: http://www.winamp.com/bin/trailer.pls?id=2
  (.pls defaults to rhythmbox)
If I open this file from firefox, I get the option to use rhythmbox, or select
an other application.
If I download it, and open it with nautilus, it offers to use rhythmbox by
default, but also has totem listed, which I manually added as an alternative to
open .pls files with.

Make firefox read out and follow the gnome/nautilus settings for a file, to
provide a better integration.