Hi, I had the same problem and found a solution -- after several hours of searching, trying, crying and whatnot: The only property you have to set is network.protocol-handler.expose.lastfm=false. Now here comes the trick: After this, you need an innocent, pure, clean and simple html link of protocol type lastfm in a document like <a href="lastfm://foo">click</a> -- no location bar, no javascript, no nothing besides html. When you click it firefox should open a dialog asking you for the application to use in order to handle the protocol. In any other case it comes up with this stupid error message ... At least this fixed it for me. Let me know if it worked. Best regards, Bianca.