This is what I did (it's a bit convoluted, but):
$ cd $HOME/.mozilla/firefox
$ cat profiles.ini
in here you will see the profiles.
Check the "Path="
points to a valid folder.
Most people will have a [Profile0]
with a Path=<??>.default
Go to that sub-folder (probably the only one)
e.g. if Path=k38lek41.default
$ cd k38lek41.default
in there you have a mimeTypes.rdf
which you can edit.
Open it and search for the mime type x-bittorrent
(You can google your the mime type) or just try torrent
(I was fixing shoutcast playlists which are x-scpls
, less obvious!)
Change the NC:useSystemDefault="false"
Now it will open in whatever KDE or Gnome has set the default app and forget Firefox.
Tested in Kubuntu (KDE).
You can also change whatever you find in NC:path="..."
to point to your favourite client app.
Exit Firefox with File->Quit and start again.
Like I said, It was convoluted, but it did work.
!! Be warned that there may be several entries for the same mime type. !!
I think Firefox uses the first match, but change them all to be safe.
Mail me if you need more help.