Configure Firefox for Magnet external protocol

Make firefox open magnet protocol use xdg-open.

1. Open Firefox and type in about:config in the Address Bar and hit Enter.
2. Type in enter handler.expose in the search box at the top of the list.
3. right click — New — Boolean
4. Enter the preference name network.protocol-handler.expose.magnet
5. Set its value to false
6. Click on a magnet link and you should see Firefox’s Launch Application Choose Dialog
7. Select /usr/bin/xdg-open.