function fixedMenu() {
  var menu = document.getElementById("menu").firstChild;
  while(menu.nodeName != 'UL') menu = menu.nextSibling;
  if(document.defaultView && document.defaultView.getComputedStyle) {
    var style = document.defaultView.getComputedStyle(menu, null);
    var top = parseFloat(style.getPropertyValue("top"));
    var height = parseFloat(style.getPropertyValue("height"));
    if(window.innerHeight > (top + height)) menu.style.position="fixed";
  }
  else if(menu.currentStyle) {
    var top = parseFloat(menu.currentStyle["top"]);
    var height = parseFloat(menu.offsetHeight);
    if(document.body.offsetHeight > (top + height)) menu.style.position="fixed";
  }
}
if(typeof maxWidth != 'function') window.onload=fixedMenu;