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