I would suggest changing the following CSS rule:

div#menu a:hover {
  border-bottom: 3px solid #FF5A00;
  padding-bottom: 0;
}

into:

div#menu a:hover, div#menu a.active {
  border-bottom: 3px solid #FF5A00;
  padding-bottom: 0;
}

This would make primary links highlighted when active. A simple change which dramatically improve menu usability.