The row of the listbox are not aligned with the head (Firefox 11 only)

<zk>
	<listbox vflex="true">
		<listhead>
			<listheader label="col" width="30px" />
			<listheader label="col" hflex="1" />
			<listheader label="col" hflex="1" />
		</listhead>
		<listitem forEach="1,2,3,4,5">
			<listcell forEach="1,2,3" label="item ${each}" />
		</listitem>
	</listbox>
</zk>