test.zul

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<zk>
<window title="new page title" border="normal">
<timebox></timebox>
</window>
</zk>

How to reproduce the issue

• view the test.zul in mobile browser or
• view the test.zul in firefox "Responsive design mode" and choose an specific device

In the browser console it will show:
"TypeError: zul.Auxbutton is not a constructor"