diff -r 000000000000 -r 6474c204b198 toolkit/devtools/server/actors/preference.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/server/actors/preference.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,126 @@
+/* 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/. */
+
+const {Cc, Ci, Cu, CC} = require("chrome");
+const protocol = require("devtools/server/protocol");
+const {Arg, method, RetVal} = protocol;
+const {Promise: promise} = Cu.import("resource://gre/modules/Promise.jsm", {});
+
+Cu.import("resource://gre/modules/Services.jsm");
+
+exports.register = function(handle) {
+  handle.addGlobalActor(PreferenceActor, "preferenceActor");
+};
+
+exports.unregister = function(handle) {
+};
+
+let PreferenceActor = protocol.ActorClass({
+  typeName: "preference",
+
+  getBoolPref: method(function(name) {
+    return Services.prefs.getBoolPref(name);
+  }, {
+    request: { value: Arg(0) },
+    response: { value: RetVal("boolean") }
+  }),
+
+  getCharPref: method(function(name) {
+    return Services.prefs.getCharPref(name);
+  }, {
+    request: { value: Arg(0) },
+    response: { value: RetVal("string") }
+  }),
+
+  getIntPref: method(function(name) {
+    return Services.prefs.getIntPref(name);
+  }, {
+    request: { value: Arg(0) },
+    response: { value: RetVal("number") }
+  }),
+
+  getAllPrefs: method(function() {
+    let prefs = {};
+    Services.prefs.getChildList("").forEach(function(name, index) {
+      // append all key/value pairs into a huge json object.
+      try {
+        let value;
+        switch (Services.prefs.getPrefType(name)) {
+          case Ci.nsIPrefBranch.PREF_STRING:
+            value = Services.prefs.getCharPref(name);
+            break;
+          case Ci.nsIPrefBranch.PREF_INT:
+            value = Services.prefs.getIntPref(name);
+            break;
+          case Ci.nsIPrefBranch.PREF_BOOL:
+            value = Services.prefs.getBoolPref(name);
+            break;
+          default:
+        }
+        prefs[name] = {
+          value: value,
+          hasUserValue: Services.prefs.prefHasUserValue(name)
+        };
+      } catch (e) {
+        // pref exists but has no user or default value
+      }
+    });
+    return prefs;
+  }, {
+    request: {},
+    response: { value: RetVal("json") }
+  }),
+
+  setBoolPref: method(function(name, value) {
+    Services.prefs.setBoolPref(name, value);
+    Services.prefs.savePrefFile(null);
+  }, {
+    request: { name: Arg(0), value: Arg(1) },
+    response: {}
+  }),
+
+  setCharPref: method(function(name, value) {
+    Services.prefs.setCharPref(name, value);
+    Services.prefs.savePrefFile(null);
+  }, {
+    request: { name: Arg(0), value: Arg(1) },
+    response: {}
+  }),
+
+  setIntPref: method(function(name, value) {
+    Services.prefs.setIntPref(name, value);
+    Services.prefs.savePrefFile(null);
+  }, {
+    request: { name: Arg(0), value: Arg(1) },
+    response: {}
+  }),
+
+  clearUserPref: method(function(name) {
+    Services.prefs.clearUserPref(name);
+    Services.prefs.savePrefFile(null);
+  }, {
+    request: { name: Arg(0) },
+    response: {}
+  }),
+});
+
+let PreferenceFront = protocol.FrontClass(PreferenceActor, {
+  initialize: function(client, form) {
+    protocol.Front.prototype.initialize.call(this, client);
+    this.actorID = form.preferenceActor;
+    client.addActorPool(this);
+    this.manage(this);
+  },
+});
+
+const _knownPreferenceFronts = new WeakMap();
+
+exports.getPreferenceFront = function(client, form) {
+  if (_knownPreferenceFronts.has(client))
+    return _knownPreferenceFronts.get(client);
+
+  let front = new PreferenceFront(client, form);
+  _knownPreferenceFronts.set(client, front);
+  return front;
+};