In some cases, you may want to use an external application when opening certain file types in Mozilla Firefox instead of using the default plugin. You can do this by editing your firefox preferences as follows:

1. Exit any currently running firefox

2. First you need to determine the mime type for the application. These are listed in /etc/mime.types. For example, if you wanted to do this for pdf files:

   % grep pdf /etc/mime.types
   application/pdf pdf

   So, for this example the mime type is application/pdf

3. You must then locate the prefs.js file for your firefox profile. You can do this by running:

   find ~/.mozilla/firefox -name prefs.js

   You may have more than one copy of this file if you have multiple profiles. In general, the default version will be in a directory that has "default" in the name.

4. Once you have located your prefs.js file, edit this file with any editor (emacs, vi, pico, etc) and add a user_pref like like:

   user_pref("plugin.disable_full_page_plugin_for_types", "MIME_TYPE_LIST");

   where you replace MIME_TYPE_LIST with a comma separated list of the mime types. For example, if you wanted to do this for mp3 and pdf files, you would add:

   user_pref("plugin.disable_full_page_plugin_for_types", "audio/mpeg,application/pdf");

5. Restart firefox and the first time you encounter a file of this type it should ask you what action you want to take. You can just enter the external application you want to use (eg. /usr/bin/gmplayer or /usr/bin/acroread). You can also check the box to always use this same application so you are not prompted again (but you should be sure it works before you do this).

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