My Ajax.js does not work in Mozilla Firefox

This is my Ajax.js, this code only work with IE8 or less but in Mozilla Firefox 3.6 doesn't work correctly.

function getXMLHTTPRequest() {
var req;
try {
    req = new XMLHttpRequest();
} catch(err1) {
    try {
        req = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (err2) {
        try {
            req = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (err3) {
                req = false;
            }
        }
    }
    return req;
}

HTML:

What is the mistake ?

 

try adding this to your code:

if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
req =new XMLHttpRequest();
}
else
{// code for IE6, IE5
req =new ActiveXObject("Microsoft.XMLHTTP");
}