Append a listitem to the listbox will cause js error (Firefox 4 above only)

 
<zk>
	<button label="add item">
		<attribute name="onClick"><![CDATA[
		Listitem item = new Listitem("item");
		lb.appendChild(item);
		item.setSelected(true);
	]]></attribute>
	</button>
	<bandbox>
		<bandpopup>
			<listbox id="lb"/>
		</bandpopup>
	</bandbox>
</zk>