Mootools: How to make cross-browser chose option menu?

Question

Mootools: How to make cross-browser chose option menu?

1 show just selected option
2 onclick on v show all option list (timeout delay)
3 onclick on different option, replace selected option

<ul>
    <li class="selected">A<span>v</span></li>
    <li>B</li>
    <li>C</li>
    <li>D</li>
</ul>

Thanks very, very much!