How do I make the menu expand in the browser

How do I configure my menu that it will expand/collapse in the browser without a roundtrip to the server?
My site www.lotusclubholland.nl has on the left side of the page a menu with submenus. When I click on one of the main menu items I would like that the submenu items are displayed directly by the browser. Now there is an additional roundtrip to the server before the menu is expanded. I do see in the source all submenu items but these are not directly shown when I click on them.

Hi there,
>> Menu Module > Advaced > Always show Submenu = YES