Ajax in firefox - can't find solution on the net

this is my js code:

$(document).ready(function (e) {
    $("#f1").on('submit',(function(e) {
        
                var ActionType = getParameterByName('t');
                var projId = getParameterByName('pj');
                var QsId = getParameterByName('s');
                
                var urlString = "uploader.php?t=";
                urlString +=ActionType;
                urlString +="&pj=";
                urlString +=projId;
                urlString +="&s=";
                urlString +=QsId;
                
                
        //e.preventDefault();
        $.ajax({
            url: urlString, 
            type: "POST",             
            data: new FormData(this), 
            contentType: false,       
            cache: false,             
            processData:false,        
            success: function(data)   
            {
                 //alert(callback); //Need to be changed
            }
        });
    }));
});
 //This function gets the parameter in the URL (GET) by name
function getParameterByName(name) {
    name = name.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
    var regex = new RegExp("[\\?&]" + name + "=([^&#]*)"),
        results = regex.exec(location.search);
    return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}

Firebug:

Accept / Accept-Encoding gzip, deflate Accept-Language en-US,en;q=0.5 Content-Length 1198 Content-Type multipart/form-data; boundary=---------------------------266932244324698 User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0 X-Requested-With XMLHttpRequest

I really can't understand the problem. Everything works perfect in Chrome and IE but not in FF

EDIT: