как-то так.
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<select id="select">
<option value='Один'>Один</option>
<option value='Два'>Два</option>
<option value='Три'>Три</option>
</select>
</body>
<script type="text/javascript">
var select = document.getElementById("select"),
select_open = false;
select.onclick = function() {
select_open = !select_open ? document.addEventListener('mouseup', waitForCloseClick, false)||true : false;
}
select.onmouseup = function(e) {
e.stopPropagation();
}
function waitForCloseClick() {
alert(123);
document.removeEventListener('mouseup', waitForCloseClick, false);
setTimeout(function(){
select_open = false;
},1);
}
</script>
</html>