function InitOverlay()
{
    var overlayDiv = document.getElementById("divOverlay");

    var pageWidth = 0;
    var pageHeight = 0;
    
    if (window.innerHeight && window.scrollMaxY ) // Firefox
    {
        pageWidth = window.innerWidth + window.scrollMaxX;
        pageHeight = window.innerHeight + window.scrollMaxY;
    }
    else if (document.body.scrollHeight > document.body.offsetHeight) // all but Explorer Mac
    {
        pageWidth = document.body.scrollWidth;
        pageHeight = document.body.scrollHeight;
    }
    else // works in Explorer 6 Strict, Mozilla (not FF) and Safari
    {
        pageWidth = document.body.offsetWidth + document.body.offsetLeft;
        pageHeight = document.body.offsetHeight + document.body.offsetTop;
    }

    overlayDiv.style.width = pageWidth.toString() + "px";
    overlayDiv.style.height = pageHeight.toString() + "px";
}

InitOverlay();

window.onresize = InitOverlay;