var yWithScroll;

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;
}