function popup(url) {
    var width = 360;
    var height = 520;
    var left = (screen.width - width) / 2;
    var top = (screen.height - height) / 2;
    var params = 'width=' + width + ', height=' + height;
    params += ', top=' + top + ', left=' + left;
    params += ', directories=no';
    params += ', location=no';
    params += ', menubar=no';
    params += ', resizable=no';
    params += ', scrollbars=no';
    params += ', status=no';
    params += ', toolbar=no';
    var randomnumber = Math.floor(Math.random() * 1000)
    newwin = window.open(url, 'windowname' + randomnumber, params);
    if (window.focus) { newwin.focus() }
    return false;
}