diff -r 000000000000 -r 6474c204b198 browser/metro/base/content/helperui/ItemPinHelper.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/metro/base/content/helperui/ItemPinHelper.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,59 @@
+// -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; -*-
+/* 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/. */
+
+"use strict";
+
+function ItemPinHelper(aUnpinnedPrefName) {
+  this._prefKey = aUnpinnedPrefName;
+}
+
+// Cache preferences on a static variable shared
+// by all instances registered to the same pref key.
+ItemPinHelper._prefValue = {};
+
+ItemPinHelper.prototype = {
+  _getPrefValue: function _getPrefValue() {
+    if (ItemPinHelper._prefValue[this._prefKey])
+      return ItemPinHelper._prefValue[this._prefKey];
+
+    try {
+      // getComplexValue throws if pref never set. Really.
+      let prefValue = Services.prefs.getComplexValue(this._prefKey, Ci.nsISupportsString);
+      ItemPinHelper._prefValue[this._prefKey] = JSON.parse(prefValue.data);
+    } catch(e) {
+      ItemPinHelper._prefValue[this._prefKey] = [];
+    }
+
+    return ItemPinHelper._prefValue[this._prefKey];
+  },
+
+  _setPrefValue: function _setPrefValue(aNewValue) {
+    let stringified = Cc["@mozilla.org/supports-string;1"].createInstance(Ci.nsISupportsString);
+    stringified.data = JSON.stringify(aNewValue);
+
+    Services.prefs.setComplexValue(this._prefKey, Ci.nsISupportsString, stringified);
+    ItemPinHelper._prefValue[this._prefKey] = aNewValue;
+  },
+
+  isPinned: function isPinned(aItemId) {
+    // Bookmarks are visible on StartUI (pinned) by default
+    return this._getPrefValue().indexOf(aItemId) === -1;
+  },
+
+  setUnpinned: function setPinned(aItemId) {
+    let unpinned = this._getPrefValue();
+    unpinned.push(aItemId);
+    this._setPrefValue(unpinned);
+  },
+
+  setPinned: function unsetPinned(aItemId) {
+    let unpinned = this._getPrefValue();
+
+    let index = unpinned.indexOf(aItemId);
+    unpinned.splice(index, 1);
+
+    this._setPrefValue(unpinned);
+  },
+}