diff -r 000000000000 -r 6474c204b198 mobile/android/base/PrefsHelper.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/PrefsHelper.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,193 @@
+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * 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/. */
+
+package org.mozilla.gecko;
+
+import org.mozilla.gecko.util.GeckoEventListener;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import android.util.Log;
+import android.util.SparseArray;
+
+import java.util.ArrayList;
+
+/**
+ * Helper class to get/set gecko prefs.
+ */
+public final class PrefsHelper {
+    private static final String LOGTAG = "GeckoPrefsHelper";
+
+    private static boolean sRegistered = false;
+    private static final SparseArray<PrefHandler> sCallbacks = new SparseArray<PrefHandler>();
+    private static int sUniqueRequestId = 1;
+
+    public static int getPref(String prefName, PrefHandler callback) {
+        return getPrefsInternal(new String[] { prefName }, callback);
+    }
+
+    public static int getPrefs(String[] prefNames, PrefHandler callback) {
+        return getPrefsInternal(prefNames, callback);
+    }
+
+    public static int getPrefs(ArrayList<String> prefNames, PrefHandler callback) {
+        return getPrefsInternal(prefNames.toArray(new String[prefNames.size()]), callback);
+    }
+
+    private static int getPrefsInternal(String[] prefNames, PrefHandler callback) {
+        int requestId;
+        synchronized (PrefsHelper.class) {
+            ensureRegistered();
+
+            requestId = sUniqueRequestId++;
+            sCallbacks.put(requestId, callback);
+        }
+
+        GeckoEvent event;
+        if (callback.isObserver()) {
+            event = GeckoEvent.createPreferencesObserveEvent(requestId, prefNames);
+        } else {
+            event = GeckoEvent.createPreferencesGetEvent(requestId, prefNames);
+        }
+        GeckoAppShell.sendEventToGecko(event);
+
+        return requestId;
+    }
+
+    private static void ensureRegistered() {
+        if (sRegistered) {
+            return;
+        }
+
+        GeckoAppShell.getEventDispatcher().registerEventListener("Preferences:Data", new GeckoEventListener() {
+            @Override public void handleMessage(String event, JSONObject message) {
+                try {
+                    PrefHandler callback;
+                    synchronized (PrefsHelper.class) {
+                        try {
+                            int requestId = message.getInt("requestId");
+                            callback = sCallbacks.get(requestId);
+                            if (callback != null && !callback.isObserver()) {
+                                sCallbacks.delete(requestId);
+                            }
+                        } catch (Exception e) {
+                            callback = null;
+                        }
+                    }
+                    if (callback == null) {
+                        Log.d(LOGTAG, "Preferences:Data message had an unknown requestId; ignoring");
+                        return;
+                    }
+
+                    JSONArray jsonPrefs = message.getJSONArray("preferences");
+                    for (int i = 0; i < jsonPrefs.length(); i++) {
+                        JSONObject pref = jsonPrefs.getJSONObject(i);
+                        String name = pref.getString("name");
+                        String type = pref.getString("type");
+                        try {
+                            if ("bool".equals(type)) {
+                                callback.prefValue(name, pref.getBoolean("value"));
+                            } else if ("int".equals(type)) {
+                                callback.prefValue(name, pref.getInt("value"));
+                            } else if ("string".equals(type)) {
+                                callback.prefValue(name, pref.getString("value"));
+                            } else {
+                                Log.e(LOGTAG, "Unknown pref value type [" + type + "] for pref [" + name + "]");
+                            }
+                        } catch (Exception e) {
+                            Log.e(LOGTAG, "Handler for preference [" + name + "] threw exception", e);
+                        }
+                    }
+                    callback.finish();
+                } catch (Exception e) {
+                    Log.e(LOGTAG, "Error handling Preferences:Data message", e);
+                }
+            }
+        });
+        sRegistered = true;
+    }
+
+    public static void setPref(String pref, Object value) {
+        if (pref == null || pref.length() == 0) {
+            throw new IllegalArgumentException("Pref name must be non-empty");
+        }
+
+        try {
+            JSONObject jsonPref = new JSONObject();
+            jsonPref.put("name", pref);
+            if (value instanceof Boolean) {
+                jsonPref.put("type", "bool");
+                jsonPref.put("value", ((Boolean)value).booleanValue());
+            } else if (value instanceof Integer) {
+                jsonPref.put("type", "int");
+                jsonPref.put("value", ((Integer)value).intValue());
+            } else {
+                jsonPref.put("type", "string");
+                jsonPref.put("value", String.valueOf(value));
+            }
+
+            GeckoEvent event = GeckoEvent.createBroadcastEvent("Preferences:Set", jsonPref.toString());
+            GeckoAppShell.sendEventToGecko(event);
+        } catch (JSONException e) {
+            Log.e(LOGTAG, "Error setting pref [" + pref + "]", e);
+        }
+    }
+
+    public static void removeObserver(int requestId) {
+        if (requestId < 0) {
+            throw new IllegalArgumentException("Invalid request ID");
+        }
+
+        synchronized (PrefsHelper.class) {
+            PrefHandler callback = sCallbacks.get(requestId);
+            sCallbacks.delete(requestId);
+
+            if (callback == null) {
+                Log.e(LOGTAG, "Unknown request ID " + requestId);
+                return;
+            }
+        }
+
+        GeckoEvent event = GeckoEvent.createBroadcastEvent("Preferences:RemoveObserver",
+                                                           Integer.toString(requestId));
+        GeckoAppShell.sendEventToGecko(event);
+    }
+
+    public interface PrefHandler {
+        void prefValue(String pref, boolean value);
+        void prefValue(String pref, int value);
+        void prefValue(String pref, String value);
+        boolean isObserver();
+        void finish();
+    }
+
+    public static abstract class PrefHandlerBase implements PrefHandler {
+        @Override
+        public void prefValue(String pref, boolean value) {
+            Log.w(LOGTAG, "Unhandled boolean value for pref [" + pref + "]");
+        }
+
+        @Override
+        public void prefValue(String pref, int value) {
+            Log.w(LOGTAG, "Unhandled int value for pref [" + pref + "]");
+        }
+
+        @Override
+        public void prefValue(String pref, String value) {
+            Log.w(LOGTAG, "Unhandled String value for pref [" + pref + "]");
+        }
+
+        @Override
+        public void finish() {
+        }
+
+        @Override
+        public boolean isObserver() {
+            return false;
+        }
+    }
+}