difference between IE and FireFox

difference between IE and FireFox

Hi all ,
in my application we are using AJAX and JAVASCRIPT. javascript code is working in IE fine but in FIREFOX it is not working i am not able to open the page in firefox . i hav checked the firefox errorconsole for errors, There we are getting one error Xml Message Has No Properties . the following line of code showing the above error

var encStatus=xmlMessage.getElementsByTagName("encStatus")[0].firstChild.nodeValue;

but the same line of code rerutning Active as encstatus in i IE


the following function is using for gettign the values through the HttpRequest

function getXML(str,mode) {
xmlHttpRequest=setXMLHttpOb(file);
//alert('IN GetXML ');
if(mode == 3) {
xmlHttpRequest.onreadystatechange=processloadAllRequest;

} else if(mode == 39) {
xmlHttpRequest.onreadystatechange=processUpdateRequest;

} else {
xmlHttpRequest.onreadystatechange=processStageRequest;
}

xmlHttpRequest.send(str);
xmlMessage=xmlHttpRequest.responseXML;
}

if kept alert message for the xmlMessage , it is giving Object in IE but same line returning null value in FireFox