menu item in RichFaces 3.3.3.Final seems to work fine with Firefox 8. I've just tried it with live demo (http://livedemo.exadel.com/richfaces-demo/richfaces/dropDownMenu.jsf?c=dropDownMenu&tab=usage).
Thanks for the quick reply. livedemo & my code differs only in submitmode attribute and actionListener.
The actionListenes are working only if we give submitMode="ajax" and not working if we give submitMode="server".
anyhow my problem is solved by changing the submitMode to ajax.