To make FireFox launch ed2k links correctly (in aMule) you have to follow some simple steps to tell it how to handle a new external protocol. This should get rid of the dreaded "ed2k is not a registered protocol" error you were most likely getting before.

• Enter about:config in the address bar
• Right click on the list, select New, then Boolean; enter network.protocol-handler.external.ed2k as Preference Name and true as Value
• Now right click, select New and String; enter network.protocol-handler.app.ed2k as Preference Name and /usr/bin/ed2k