http://bdbits.wordpress.com/2008/07/01/unblock-a-nonstandard-port-in-firefox3/
enter about:config in the address bar, and then right-click anywhere in the lower portion of the resulting page and select New and then String from the context menu. The name you need to enter is network.security.ports.banned.override, and the value is the port(s) you want to open. If you have more than one, enter them as a comma-separated list.