function mainmenu() {
    $("#nav ul").css({ display: "none" }); // Opera Fix
    $("#nav li").hover(function() {
        $(this).children('.nav').addClass('navOn');
        $(this).find('ul:first').css({ visibility: "visible", display: "block" });
    }, function() {
        $(this).children('.nav').removeClass('navOn');
        $(this).find('ul:first').css({ visibility: "hidden", display: "none" });
    });
}

$(document).ready(function() {
    mainmenu();
});