Browser Close onUserExit.js

Hi,

This is with reference to
onUserExit jQuery Plugin
I want to use onUserExit.js
But exactly i am unable to implement.
My requirement is to know when user close the browser.
How do I know this with minimum effort.
I am using asp.net 2.0 and master page.

<script type="text/javascript" src="js/jquery.js"></script>
<script type="text/javascript" src="js/jquery.url.packed.js"></script>
<script type="text/javascript" src="js/onUserExit.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$().onUserExit({
execute: function()
{
alert("This alert was executed upon you leaving this page to another website, or when you closed the browser!");
},
internalURLs: "creations.userfirstinteractive.com ";
});

});

</script>

Now,How do I know when user close the browser.
The alert fire everytime when there is page postback.
Where to modify code ?
Those who have use this will be able to help me


Thanks

KumarHarsh