Bug 1300753 - Trigger document localization on readystate=complete

Revert "Bug 1299184 - Move translation trigger for Gecko to MozBeforeLayout"
This reverts commit 1669cd2.

src/runtime/gecko/l20n-chrome-xul.js

@@ -2,7 +2,7 @@ import { ChromeLocalizationObserver } from '../../lib/observer/chrome';
 import { XULLocalization } from '../../lib/dom/xul';
 
 import { ChromeResourceBundle } from './io';
-import { getResourceLinks, createObserve } from './util';
+import { XULDocumentReady, getResourceLinks, createObserve } from './util';
 
 Components.utils.import('resource://gre/modules/Services.jsm');
 Components.utils.import('resource://gre/modules/L10nRegistry.jsm');
@@ -63,13 +63,10 @@ function createLocalization(name, resIds) {
   document.l10n.set(name, l10n);
 
   if (name === 'main') {
-    document.addEventListener('MozBeforeLayout', () => {
+    XULDocumentReady().then(() => {
       const rootElem = document.documentElement;
       document.l10n.observeRoot(rootElem, l10n);
       document.l10n.translateRoot(rootElem, l10n);
-    }, {
-      once: true,
-      passive: true
     });
   }
 }

src/runtime/gecko/util.js

@@ -5,6 +5,19 @@ export {
   documentReady as HTMLDocumentReady, getResourceLinks
 } from '../web/util';
 
+export function XULDocumentReady() {
+  if (document.readyState !== 'uninitialized') {
+    return Promise.resolve();
+  }
+
+  return new Promise(resolve => {
+    document.addEventListener('readystatechange', function onrsc() {
+      document.removeEventListener('readystatechange', onrsc);
+      resolve();
+    });
+  });
+}
+
 export function createGetValue(bundles) {
   return function (id, args) {
     const ctx = contexts.get(bundles[0]);