diff -r 000000000000 -r 6474c204b198 addon-sdk/source/lib/sdk/l10n/html.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/addon-sdk/source/lib/sdk/l10n/html.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,111 @@
+/* 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";
+
+module.metadata = {
+  "stability": "unstable"
+};
+
+const { Ci, Cu } = require("chrome");
+const events = require("../system/events");
+const core = require("./core");
+
+const assetsURI = require('../self').data.url();
+const { Services } = Cu.import("resource://gre/modules/Services.jsm");
+
+const hideContentStyle = "data:text/css,:root {visibility: hidden !important;}";
+const hideSheetUri = Services.io.newURI(hideContentStyle, null, null);
+
+// Taken from Gaia:
+// https://github.com/andreasgal/gaia/blob/04fde2640a7f40314643016a5a6c98bf3755f5fd/webapi.js#L1470
+function translateElement(element) {
+  element = element || document;
+
+  // check all translatable children (= w/ a `data-l10n-id' attribute)
+  var children = element.querySelectorAll('*[data-l10n-id]');
+  var elementCount = children.length;
+  for (var i = 0; i < elementCount; i++) {
+    var child = children[i];
+
+    // translate the child
+    var key = child.dataset.l10nId;
+    var data = core.get(key);
+    if (data)
+      child.textContent = data;
+  }
+}
+exports.translateElement = translateElement;
+
+function onDocumentReady2Translate(event) {
+  let document = event.target;
+  document.removeEventListener("DOMContentLoaded", onDocumentReady2Translate,
+                               false);
+
+  translateElement(document);
+
+  try {
+    // Finally display document when we finished replacing all text content
+    if (document.defaultView) {
+      let winUtils = document.defaultView.QueryInterface(Ci.nsIInterfaceRequestor)
+                                         .getInterface(Ci.nsIDOMWindowUtils);
+      winUtils.removeSheet(hideSheetUri, winUtils.USER_SHEET);
+    }
+  }
+  catch(e) {
+    console.exception(e);
+  }
+}
+
+function onContentWindow(event) {
+  let document = event.subject;
+
+  // Accept only HTML documents
+  if (!(document instanceof Ci.nsIDOMHTMLDocument))
+    return;
+
+  // Bug 769483: data:URI documents instanciated with nsIDOMParser
+  // have a null `location` attribute at this time
+  if (!document.location)
+    return;
+
+  // Accept only document from this addon
+  if (document.location.href.indexOf(assetsURI) !== 0)
+    return;
+
+  try {
+    // First hide content of the document in order to have content blinking
+    // between untranslated and translated states
+    let winUtils = document.defaultView.QueryInterface(Ci.nsIInterfaceRequestor)
+                                       .getInterface(Ci.nsIDOMWindowUtils);
+    winUtils.loadSheet(hideSheetUri, winUtils.USER_SHEET);
+  }
+  catch(e) {
+    console.exception(e);
+  }
+  // Wait for DOM tree to be built before applying localization
+  document.addEventListener("DOMContentLoaded", onDocumentReady2Translate,
+                            false);
+}
+
+// Listen to creation of content documents in order to translate them as soon
+// as possible in their loading process
+const ON_CONTENT = "document-element-inserted";
+let enabled = false;
+function enable() {
+  if (!enabled) {
+    events.on(ON_CONTENT, onContentWindow);
+    enabled = true;
+  }
+}
+exports.enable = enable;
+
+function disable() {
+  if (enabled) {
+    events.off(ON_CONTENT, onContentWindow);
+    enabled = false;
+  }
+}
+exports.disable = disable;
+
+require("sdk/system/unload").when(disable);