diff --git a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
index 419d8a9302c0..b662ed8c5b46 100644
--- a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
+++ b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
@@ -331,6 +331,24 @@ SpecialPowersAPI.prototype = {
     this.wrappedJSObject.SpecialPowers._applyPrefs();
   },
 
+  addObserver: function(obs, notification, weak) {
+    var obsvc = Cc['@mozilla.org/observer-service;1']
+                   .getService(Ci.nsIObserverService);
+    obsvc.addObserver(obs, notification, weak);
+  },
+  removeObserver: function(obs, notification) {
+    var obsvc = Cc['@mozilla.org/observer-service;1']
+                   .getService(Ci.nsIObserverService);
+    obsvc.removeObserver(obs, notification);
+  },
+   
+  can_QI: function(obj) {
+    return obj.QueryInterface !== undefined;
+  },
+  do_QueryInterface: function(obj, iface) {
+    return obj.QueryInterface(Ci[iface]); 
+  },
+
   // Mimic the get*Pref API
   getBoolPref: function(aPrefName) {
     return (this._getPref(aPrefName, 'BOOL'));
diff --git a/testing/mochitest/tests/test_SpecialPowersExtension.html b/testing/mochitest/tests/test_SpecialPowersExtension.html
index ea7d80527ca1..c00c5095d1e6 100644
--- a/testing/mochitest/tests/test_SpecialPowersExtension.html
+++ b/testing/mochitest/tests/test_SpecialPowersExtension.html
@@ -81,6 +81,12 @@ function starttest(){
   ok(xhr, "createSystemXHR should not return null");
   is(xhr.readyState, XMLHttpRequest.UNSENT, "createSystemXHR should create an unsent XMLHttpRequest object");
   
+  // QueryInterface and getPrivilegedProps tests
+  is(SpecialPowers.can_QI(SpecialPowers), false);
+  ok(SpecialPowers.can_QI(window));
+  ok(SpecialPowers.do_QueryInterface(window, "nsIDOMWindow"));
+  is(SpecialPowers.getPrivilegedProps(SpecialPowers.do_QueryInterface(window, "nsIDOMWindow"), "document.nodeName"), "#document");
+  
   //try to run garbage collection
   SpecialPowers.gc();