Event.observe(document,"dom:loaded",adaptMenu);

function adaptMenu(){
    var clear = $('menu').select('.clear')[0];
    $('menu').select('li.active ul').each(function(submenu){
        clear.insert({'before':submenu});
        $(submenu).addClassName("active");
        var height = $(submenu).offsetTop + $(submenu).getHeight();
        $('menu').setStyle({'height': height + "px"})
    });    
}