function sfHover() {
  var sfEls = document.getElementById('main_nav').getElementsByTagName('li');
  for(var i=0; i<sfEls.length; i++) {
    sfEls[i].onmouseover = function() {
      this.className += ' sfhover';
    }
    sfEls[i].onmouseout = function() {
      this.className = this.className.replace(new RegExp(' sfhover\\b', ''));
    }
  }
}
if(window.attachEvent) {
  window.attachEvent('onload', sfHover);
  }