diff -r 000000000000 -r 6474c204b198 docshell/test/unit/test_privacy_transition.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/docshell/test/unit/test_privacy_transition.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,23 @@
+var gNotifications = 0;
+
+var observer = {
+  QueryInterface: function(iid) {
+    if (Ci.nsIPrivacyTransitionObserver.equals(iid) ||
+        Ci.nsISupportsWeakReference.equals(iid) ||
+        Ci.nsISupports.equals(iid))
+      return this;
+    throw Cr.NS_ERROR_NO_INTERFACE;
+  },
+  
+  privateModeChanged: function(enabled) {
+    gNotifications++;
+  }
+}
+
+function run_test() {
+  var docshell = Cc["@mozilla.org/docshell;1"].createInstance(Ci.nsIDocShell);
+  docshell.addWeakPrivacyTransitionObserver(observer);
+  docshell.QueryInterface(Ci.nsILoadContext).usePrivateBrowsing = true;
+  docshell.QueryInterface(Ci.nsILoadContext).usePrivateBrowsing = false;
+  do_check_eq(gNotifications, 2);
+}
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