diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/system/unload.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/system/unload.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,82 @@
+/* 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/. */
+
+// Parts of this module were taken from narwhal:
+//
+// http://narwhaljs.org
+
+module.metadata = {
+  "stability": "experimental"
+};
+
+const { on, off } = require('./events');
+const unloadSubject = require('@loader/unload');
+
+const observers = [];
+const unloaders = [];
+
+var when = exports.when = function when(observer) {
+  if (observers.indexOf(observer) != -1)
+    return;
+  observers.unshift(observer);
+};
+
+var ensure = exports.ensure = function ensure(obj, destructorName) {
+  if (!destructorName)
+    destructorName = "unload";
+  if (!(destructorName in obj))
+    throw new Error("object has no '" + destructorName + "' property");
+
+  let called = false;
+  let originalDestructor = obj[destructorName];
+
+  function unloadWrapper(reason) {
+    if (!called) {
+      called = true;
+      let index = unloaders.indexOf(unloadWrapper);
+      if (index == -1)
+        throw new Error("internal error: unloader not found");
+      unloaders.splice(index, 1);
+      originalDestructor.call(obj, reason);
+      originalDestructor = null;
+      destructorName = null;
+      obj = null;
+    }
+  };
+
+  // TODO: Find out why the order is inverted here. It seems that
+  // it may be causing issues!
+  unloaders.push(unloadWrapper);
+
+  obj[destructorName] = unloadWrapper;
+};
+
+function unload(reason) {
+  observers.forEach(function(observer) {
+    try {
+      observer(reason);
+    }
+    catch (error) {
+      console.exception(error);
+    }
+  });
+}
+
+when(function(reason) {
+  unloaders.slice().forEach(function(unloadWrapper) {
+    unloadWrapper(reason);
+  });
+});
+
+on('sdk:loader:destroy', function onunload({ subject, data: reason }) {
+  // If this loader is unload then `subject.wrappedJSObject` will be
+  // `destructor`.
+  if (subject.wrappedJSObject === unloadSubject) {
+    off('sdk:loader:destroy', onunload);
+    unload(reason);
+  }
+// Note that we use strong reference to listener here to make sure it's not
+// GC-ed, which may happen otherwise since nothing keeps reference to `onunolad`
+// function.
+}, true);