Please try this html. It's different between IE6 and firefox3. why?
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http:// www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <script type="text/javascript" src="jquery-1.2.6.js"></script> <script type="text/javascript"> <!-- function showSize() { var s = $("root > level5 > elem").size(); alert(s); } //--> </script> <title>test</title> </head> <body> <form id="form1" name="form1" method="post" action=""> <input type="button" name="p" id="p" value="show" onclick="showSize()" /> </form> <div style="display:none;"> <root data="a"> <level5> <elem index="0" data="b"></elem> <elem index="14" data="c"></elem> </level5> </root> </div> </body> </html>