Open page in hidden background

I'm looking for some idea why this code:

var urlpopup = "http://googl.com";
function myClickHandler() {
        if(web == true)
        setTimeout('popup(urlpopup)', 200);
    }
    //funcion para mostrar el popup 
    function popup(url){
        params = 'width='+screen.width;
        params += ', height='+screen.height;
        params += ', top=0, left=0'
        params += ', fullscreen=yes'
        params += ',_parent'
        params += ',channelmode=0'
        params += ',directories=0'
        params += ',location=0'
        params += ',menubar=0'
        params += ',resizable=0'
        params += ',status=0';
        var pu = window.open(url,'Rollassage', params);
        pu.blur()
        window.focus();
        return false;
    }

that is supposed to open a window in the background does not; the window with the url of

  

google.com

appears in the foreground, not behind the main page.