diff -r 000000000000 -r 6474c204b198 netwerk/test/unit/test_addr_in_use_error.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/netwerk/test/unit/test_addr_in_use_error.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,32 @@
+// 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();
+}