diff -r 000000000000 -r 6474c204b198 toolkit/mozapps/update/tests/unit_base_updater/marVersionDowngrade.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/mozapps/update/tests/unit_base_updater/marVersionDowngrade.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,30 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+/* Test version downgrade MAR security check */
+
+function run_test() {
+  if (!IS_MAR_CHECKS_ENABLED) {
+    return;
+  }
+
+  setupTestCommon();
+  // We don't actually care if the MAR has any data, we only care about the
+  // application return code and update.status result.
+  gTestFiles = gTestFilesCommon;
+  gTestDirs = [];
+  setupUpdaterTest(FILE_OLD_VERSION_MAR, false, false);
+
+  // Apply the MAR
+  // Note that if execv is used, the updater process will turn into the
+  // callback process, so its return code will be that of the callback
+  // app.
+  runUpdate((USE_EXECV ? 0 : 1), STATE_FAILED_VERSION_DOWNGRADE_ERROR);
+}
+
+function checkUpdateApplied() {
+  checkFilesAfterUpdateSuccess();
+  doTestFinish();
+}