If you want do it in real time, simply paste the code below somewhere inside the HTML tags:
Code:
<span id="brchk"><span>
<script>
var ua = window.navigator.userAgent;
var msie = ua.indexOf("MSIE ");
if (msie > 0 || !!navigator.userAgent.match(/Trident.*rv\:11\./))
document.getElementById("brchk").innerHTML = "<!-- two three four -->";
else
document.getElementById("brchk").innerHTML = "<!-- one two three four -->";
</script>
Since it's just a quick check, this is probably the easiest and most sensible approach.