function getPageHeight() {
    if (window.innerHeight && window.scrollMaxY) { // Firefox
        yWithScroll = window.innerHeight + window.scrollMaxY;
    } else if (document.body.scrollHeight > document.body.offsetHeight) { // all but Explorer Mac
        yWithScroll = document.body.scrollHeight;
    } else { // works in Explorer 6 Strict, Mozilla (not FF) and Safari
        yWithScroll = document.body.offsetHeight;
    }
    return yWithScroll;
}