how to clear all session in php when a page unload in php

in firefox this is not working on some computer please help me out i am also using jquery

this is the full code


the link is here

http://shaktimachinerystore.com/downloads.php

in this page i am using the code of jquery which will fire on unload of page
<script type="text/javascript">
window.onunload = dostuff();
function dostuff() {
$.get("http://shaktimachinerystore.com/clear.php");
$.ajax({url:"http://shaktimachinerystore.com/clear.php?", async:false});
alert('bye');


}
</script>
in clear.php i wrote
<!--?php session_start();
session_unset();
session_destroy();
??-->


and in downloads page to hide and show the forms and links i used


<!--?php
if(isset($_SESSION['temp'])){
echo '<div style="display:none;"?-->';
}
?>
<form name="frm1" method="post" action="downloadsmail.php" >
<!--?php
if(isset($_SESSION['temp'])){
echo '</div?-->';
}
?>

i am giving only the form tag to be precise

and below is table in variable $tableshow which will echo if session have any value


<!--?php $tableshow='<table class="maintab" border="0" cellpadding="0" cellspacing="0" style="width: 100%"?-->
<tr>
<td style="width: 40%; height: 90px; text-align: center">

<img border="0" src="images/pdfownimg_23.jpg" />
</td>
<td style="width: 31%; height: 90px; text-align: center">
<img border="0" src="images/pdfownimg_25.jpg" />
</td>
<td style="width: 33%; height: 90px; text-align: center">
<img border="0" src="images/pdfownimg_27.jpg" /></td>
</tr>
<tr>
<td style="width: 40%; height: 76px; text-align: center">
<img border="0" src="images/pdfownimg_32.jpg" /> </td>
<td style="width: 31%; height: 76px; text-align: center">
<img border="0" src="images/pdfownimg_34.jpg" /> </td>
<td style="width: 33%; height: 76px">
</td>
</tr>
<tr>
<td colspan="3" style="width: 40%;text-align:center; font-size:12px;">
Don’t have PDF reader. Click here to Download Pdf Reader.
</td>
</tr>
</table>';




if(isset($_SESSION['temp'])){

echo $tableshow;
}
?>

this is final solution

if(count($_POST)>0)
{
do whatever you want with user information - save in db or mail etc
& show download contents here
}
else
{
show form(with Post method) here, action will be downloads.php