diff -r 000000000000 -r 6474c204b198 modules/libjar/test/unit/test_bug407303.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/test/unit/test_bug407303.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,39 @@
+// Regression test for bug 407303 - A failed channel should not be checked
+// for an unsafe content type.
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+// XXX: NS_ERROR_UNKNOWN_HOST is not in Components.results
+const NS_ERROR_UNKNOWN_HOST = 0x804B001E;
+
+var listener = {
+  QueryInterface: function(iid) {
+    if (iid.equals(Ci.nsISupports) ||
+        iid.equals(Ci.nsIRequestObserver))
+      return this;
+    throw Cr.NS_ERROR_NO_INTERFACE;
+  },
+
+  onStartRequest: function(request, context) {
+  },
+
+  onDataAvailable: function(request, context, stream, offset, count) {
+    do_throw("shouldn't get data!");
+  },
+
+  onStopRequest: function(request, context, status) {
+    do_check_eq(status, NS_ERROR_UNKNOWN_HOST);
+    do_test_finished();
+  }
+};
+
+function run_test() {
+  var ios = Cc["@mozilla.org/network/io-service;1"].
+            getService(Ci.nsIIOService);
+
+  var channel = ios.newChannel("jar:http://test.invalid/test.jar!/index.html",
+                               null, null);
+  channel.asyncOpen(listener, null);
+  do_test_pending();
+}