diff -r 000000000000 -r 6474c204b198 toolkit/mozapps/extensions/test/xpinstall/browser_enabled3.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/mozapps/extensions/test/xpinstall/browser_enabled3.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,45 @@
+// ----------------------------------------------------------------------------
+// Test whether an InstallTrigger.install call fails when xpinstall is disabled
+function test() {
+  Harness.installDisabledCallback = install_disabled;
+  Harness.installBlockedCallback = allow_blocked;
+  Harness.installConfirmCallback = confirm_install;
+  Harness.setup();
+
+  Services.prefs.setBoolPref("xpinstall.enabled", false);
+
+  var triggers = encodeURIComponent(JSON.stringify({
+    "Unsigned XPI": TESTROOT + "unsigned.xpi"
+  }));
+  gBrowser.selectedTab = gBrowser.addTab();
+  gBrowser.selectedBrowser.addEventListener("load", function() {
+    gBrowser.selectedBrowser.removeEventListener("load", arguments.callee, true);
+    // Allow the in-page load handler to run first
+    executeSoon(page_loaded);
+  }, true);
+  gBrowser.loadURI(TESTROOT + "installtrigger.html?" + triggers);
+}
+
+function install_disabled(installInfo) {
+  ok(true, "Saw installation disabled");
+}
+
+function allow_blocked(installInfo) {
+  ok(false, "Should never see the blocked install notification");
+  return false;
+}
+
+function confirm_install(window) {
+  ok(false, "Should never see an install confirmation dialog");
+  return false;
+}
+
+function page_loaded() {
+  Services.prefs.clearUserPref("xpinstall.enabled");
+
+  var doc = gBrowser.contentDocument;
+  is(doc.getElementById("return").textContent, "false", "installTrigger should have not been enabled");
+  gBrowser.removeCurrentTab();
+  Harness.finish();
+}
+// ----------------------------------------------------------------------------