m4a1fox

    $(function() {
        var box = $('#messagelist'); // float-fixed block

        var top = box.offset().top - parseFloat(box.css('marginTop').replace(/auto/, 0));
        $(window).scroll(function(){
            var windowpos = $(window).scrollTop();
            if(windowpos < top) {
                box.css('position', 'static');
            } else {
                box.css('position', 'fixed');
                box.css('top', 0);
            }
        });
    });