For a little background; users of our kiosks need to be able to view files hosted on an external webpage. These are PDF files, but unfortunately something seems to be wrong with how the MIMEtype of the file is defined as firefox doesn't realise it's a PDF and so doesn't know what to do with it. This is what it shows when I open within the desktop edition;

If (on the desktop edition) I set "Open with" and select /usr/bin/firefox and click "Do this automagically" then it happily opens in Firefox;

This results in a row being added to the applications list in the preferences;

As far as I'm aware, this is saved in the Firefox profile within 'mimeTypes.rdf'.
What I'd like to know is if there is any way of setting this on the kiosk through the about:config parameter, or will it require editting one of the modules we use to build the kiosk?
Thanks for your help.