Issue with Firefox using executeQueryAsync

I have ECMA script code

{

var clientContext = SP.ClientContext.get_current();

    var webSite = clientContext.get_web();

    var lists = webSite.get_lists();
    
    var mailBoxList = lists.getByTitle("vacation");
    clientContext.load(mailBoxList);
    var itemCreationInfo = new SP.ListItemCreationInformation();

    var listItem = mailBoxList.addItem(itemCreationInfo);
    
    listItem.set_item("Title", "subject");
    listItem.set_item("Message", "message");

    
    listItem.update();

    clientContext.load(listItem);

    clientContext.executeQueryAsync(Function.createDelegate(this, this.onSuccees),Function.createDelegate(this, this.onFail));
  

} 

onSuccees = function (sender, args) {
//alert("Success");
}


onFail = function (sender, args) {
    alert('failed to send Email. Error:' + args.get_message());
}

The above code is working fine in IE and Chrome but does not work in FireFox.

Any idea?