How to open a popup in Mozilla

<script type="text/javascript">
    function openPopUp()
                    {
                        var popUrl = 'EditUser.aspx';
                    var name = 'popUp';
                    var appearence ='dependent=yes,menubar=no,resizable=yes,'+
                                          'status=no,toolbar=no,titlebar=no,' +
                                          'left=40,top=150,width=1300px,height=500px';
                    var openWindow = window.open(popUrl, name, appearence);
                    openWindow.focus();
                    }
    </script>

protected void Page_Load(object sender, EventArgs e)
    {
        btn_Edit.Attributes.Add("onclick", "openPopUp('EditUser.aspx')");
        
        
    }

//write code on dropdown_selectedindexchanged
response.write("<script>alert('your massage')<script>"); 
</script></script>