in IE, document.all is working but not in firefox, in firefox have to use document.getElementById instead IE: document.all.tab1Div.style.display='none'; document.all.tab2Div.style.display=''; document.all.tab3Div.style.display='none'; document.all.li1Div.className = ''; document.all.li2Div.className = "selected"; document.all.li3Div.className = ''; Firefox: document.getElementById('tab1Div').style.display='none'; document.getElementById('tab2Div').style.display=''; document.getElementById('tab3Div').style.display='none'; document.getElementById('li1Div').className = ""; document.getElementById('li2Div').className = 'selected'; document.getElementById('li3Div').className = '';