FCKeditor percentage height does not work on Firefox

<?page id="testZul" title=" New ZUL Title" cacheable="false" 
	language="xul/html" zscriptLanguage="Java" contentType="text/html;charset=UTF-8"?>

<zk xmlns="http://www.zkoss.org/2005/zul"
	xmlns:h="http://www.w3.org/1999/xhtml" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://www.zkoss.org/2005/zul http://www.zkoss.org/2005/zul/zul.xsd">
<borderlayout>
	<center border="none">
		<fckeditor id="fckeditor" customConfigurationsPath="/editors/fckconfig.js" width="100%" height="100%" />
	</center>
</borderlayout>
</zk>