Don't bind the debugger server to the default port

I see that the debugger server is not used for local profiling, but the add-on opens a listener on port 6000 anyway. This causes problems for users who have the add-on installed and try to connect the developer tools to remote instances, since the tools connect to the Firefox instance that grabbed port 6000.

This patch leaves the remote profiling support disabled as before, but makes sure that the local transport is used for local profiling, which doesn't use network sockets.