var xMax = screen.width, yMax = self.screen.availHeight;

if (document.body.clientWidth)
{
  lnBodyClientWidth=document.body.clientWidth 
  lnBodyClientHeight=document.body.clientHeight 
}
else
{
  lnBodyClientWidth=window.innerWidth
  lnBodyClientHeight=window.innerHeight
} 

xOffset = (xMax - lnBodyClientWidth)/2, yOffset = (yMax - lnBodyClientHeight)/2;
self.moveTo(xOffset,yOffset)