var currheight;
var currwidth;

window.onresize = function(){

  if (parseInt(navigator.appVersion)>3) {
    if (navigator.appName=="Netscape") {
      winW = window.innerWidth;
      winH = window.innerHeight;
    }
    if (navigator.appName.indexOf("Microsoft")!=-1) {
      winW = document.body.offsetWidth;
      winH = document.body.offsetHeight;
    }
  }

  if (currheight != winH || currwidth != winW) {
    pos("popupScreenFront");	
  }
  currheight = winH;
  currwidth = winW;
}

function pos(y) {

  document.getElementById(y).style.top = document.documentElement.offsetHeight/2-240 + 'px';
  document.getElementById(y).style.left = document.body.offsetWidth/2-320 + 'px';
}

pos("popupScreenFront");