Try to google zk forum
the 1st link will redirect to http://www.zkoss.org/forum/index.zul
then the main content is not rendered.
If navigate to http://ww.zkoss.org/forum
then the URL will become http://www.zkoss.org/forum/index.zul#path%3Dindex%3B
Ubuntu Intrepid with Firefox 3.0.x