diff -r 000000000000 -r 6474c204b198 toolkit/modules/WindowsRegistry.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/modules/WindowsRegistry.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,50 @@
+/* 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";
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+this.EXPORTED_SYMBOLS = ["WindowsRegistry"];
+
+const WindowsRegistry = {
+  /**
+   * Safely reads a value from the registry.
+   *
+   * @param aRoot
+   *        The root registry to use.
+   * @param aPath
+   *        The registry path to the key.
+   * @param aKey
+   *        The key name.
+   * @return The key value or undefined if it doesn't exist.  If the key is
+   *         a REG_MULTI_SZ, an array is returned.
+   */
+  readRegKey: function(aRoot, aPath, aKey) {
+    const kRegMultiSz = 7;
+    let registry = Cc["@mozilla.org/windows-registry-key;1"].
+                   createInstance(Ci.nsIWindowsRegKey);
+    try {
+      registry.open(aRoot, aPath, Ci.nsIWindowsRegKey.ACCESS_READ);
+      if (registry.hasValue(aKey)) {
+        let type = registry.getValueType(aKey);
+        switch (type) {
+          case kRegMultiSz:
+            // nsIWindowsRegKey doesn't support REG_MULTI_SZ type out of the box.
+            let str = registry.readStringValue(aKey);
+            return [v for each (v in str.split("\0")) if (v)];
+          case Ci.nsIWindowsRegKey.TYPE_STRING:
+            return registry.readStringValue(aKey);
+          case Ci.nsIWindowsRegKey.TYPE_INT:
+            return registry.readIntValue(aKey);
+          default:
+            throw new Error("Unsupported registry value.");
+        }
+      }
+    } catch (ex) {
+    } finally {
+      registry.close();
+    }
+    return undefined;
+  },
+};