Firefox (or Seamonkey, which is based on Firefox) is a great Web browser, but it’s mime-handling under Linux is just plain annoying sometimes. A nice trick that can improve the integration of Firefox into your Desktop Environment is using xdg-open to open file links from Firefox’s Download window. But a magnet link (a type of link to a torrent that is getting increasingly popular) is a little more “exotic” for the moment, and requires a different trick:
1. Fire up Firefox and type about:config in the address bar.
2. Right click on an entry > New > Boolean
3. Enter: network.protocol-handler.expose.magnet
4. Choose False as its value
Done! Now, the next time you click on a magnet link, Firefox will bring up the familiar dialog for choosing an application to handle the filetype, say, /usr/bin/transmission-gtk, and have Firefox remember your choice.