The menu uses the ultra efficient Nekkidblogger menu framework, the same as I used for the horizontal CSS drop menu. It uses an accessible, standard UL (unordered list) classed with classes for the levels of the menu. The CSS is light, simple and very fast.
It is the most efficient menu there is: no complex CSS rules with long lists of descendant selectors and a clear separation between presentational and structural elements.
The menu has been tested extensively and works well in all modern browsers: Chrome, Firefox, Internet Explorer from IE 7 and up, as well as Safari and Opera. For IE6 some fixes are required. You can find these, along with the markup and CSS for this menu, in the online demo.
See also the most recent version of this menu system, where the right-most drop-downs float left instead of right.