The Tor Browser / file revision

 // Opening a second listening socket on the same address as an extant

 // socket should elicit NS_ERROR_SOCKET_ADDRESS_IN_USE on non-Windows

 // machines.

 const CC = Components.Constructor;

 const ServerSocket = CC("@mozilla.org/network/server-socket;1",

                         "nsIServerSocket",

                         "init");

 function testAddrInUse()

 {

   // Windows lets us have as many sockets listening on the same address as

   // we like, evidently.

   if ("@mozilla.org/windows-registry-key;1" in Cc) {

     return;

   }

   // Create listening socket:

   // any port (-1), loopback only (true), default backlog (-1)

   let listener = ServerSocket(-1, true, -1);

   do_check_true(listener instanceof Ci.nsIServerSocket);

   // Try to create another listening socket on the same port, whatever that was.

   do_check_throws_nsIException(() => ServerSocket(listener.port, true, -1),

                                "NS_ERROR_SOCKET_ADDRESS_IN_USE");

 }

 function run_test()

 {

   testAddrInUse();

 }