Comment 45 for bug 133133

firefox version: 3.1b3
De: Kde 3.5

I'm using archlinux and i haven't any problem.

I think it's just a matter of mimetypes (located at: ~/.mozilla/firefox/ProfileName/mimeTypes.rdf )
Attached you'll find mine which uses /usr/bin/xdg-open, but if "file" is defined, you can easilly go through:
Menu Edit, Preferences, Applications, scroll down until "file", and select something useful for you in the second column.