--- a/accessible/src/jsat/AccessFu.jsm
+++ b/accessible/src/jsat/AccessFu.jsm
@@ -42,16 +42,24 @@ var AccessFu = {
     this.prefsBranch = Cc['@mozilla.org/preferences-service;1']
       .getService(Ci.nsIPrefService).getBranch('accessibility.accessfu.');
     this.prefsBranch.addObserver('activate', this, false);
     this.prefsBranch.addObserver('explorebytouch', this, false);
 
     if (Utils.MozBuildApp == 'mobile/android')
       Services.obs.addObserver(this, 'Accessibility:Settings', false);
 
+    if (Utils.MozBuildApp == 'b2g')
+      aWindow.addEventListener(
+        'ContentStart',
+        (function(event) {
+           let content = aWindow.shell.contentBrowser.contentWindow;
+           content.addEventListener('mozContentEvent', this, false, true);
+         }).bind(this), false);
+
     this._processPreferences();
   },
 
   /**
    * Start AccessFu mode, this primarily means controlling the virtual cursor
    * with arrow keys.
    */
   _enable: function _enable() {
@@ -187,16 +195,24 @@ var AccessFu = {
         break;
       }
       case 'scroll':
       case 'resize':
       {
         this.presenters.forEach(function(p) { p.viewportChanged(); });
         break;
       }
+      case 'mozContentEvent':
+      {
+        if (aEvent.detail.type == 'accessibility-screenreader') {
+          let pref = aEvent.detail.enabled + 0;
+          this._processPreferences(pref, pref);
+        }
+        break;
+      }
     }
   },
 
   observe: function observe(aSubject, aTopic, aData) {
     switch (aTopic) {
       case 'Accessibility:Settings':
         this._processPreferences(JSON.parse(aData).enabled + 0,
                                  JSON.parse(aData).exploreByTouch + 0);