--- a/testing/marionette/client/marionette/marionette_test.py
+++ b/testing/marionette/client/marionette/marionette_test.py
@@ -474,17 +474,17 @@ if((navigator.mozSettings == undefined) 
 let setReq = navigator.mozSettings.createLock().set({'lockscreen.enabled': false});
 setReq.onsuccess = function() {
     let appsReq = navigator.mozApps.mgmt.getAll();
     appsReq.onsuccess = function() {
         let apps = appsReq.result;
         for (let i = 0; i < apps.length; i++) {
             let app = apps[i];
             if (app.manifest.name === 'Test Container') {
-                let manager = window.wrappedJSObject.AppWindowManager || window.wrappedJSObject.WindowManager;
+                let manager = window.wrappedJSObject.appWindowManager || window.wrappedJSObject.AppWindowManager;
                 if (!manager) {
                     marionetteScriptFinished(false);
                     return;
                 }
                 manager.kill(app.origin);
                 marionetteScriptFinished(true);
                 return;
             }

--- a/testing/web-platform/harness/wptrunner/browsers/b2g.py
+++ b/testing/web-platform/harness/wptrunner/browsers/b2g.py
@@ -228,17 +228,17 @@ class B2GExecutorBrowser(ExecutorBrowser
     def use_cert_app(self):
         """Start the app used to run the tests"""
         self.executor.logger.info("Homescreen loaded")
         self.gaia_apps.launch("CertTest App")
 
     def wait_for_homescreen(self, timeout):
         self.executor.logger.info("Waiting for homescreen")
         self.marionette.execute_async_script("""
-let manager = window.wrappedJSObject.AppWindowManager || window.wrappedJSObject.WindowManager;
+let manager = window.wrappedJSObject.appWindowManager || window.wrappedJSObject.AppWindowManager;
 let app = null;
 if (manager) {
   app = ('getActiveApp' in manager) ? manager.getActiveApp() : manager.getCurrentDisplayedApp();
 }
 if (app) {
   log('Already loaded home screen');
   marionetteScriptFinished();
 } else {