It looks like the accordion has an "active" property to set the active window... so:
Initialize a accordion with the active option specified.
$( ".selector" ).accordion({ active: 2 });
would set the second value to the active one. You could pass that value in through the url and write it dynamically with <?php echo(); ?> like:
$( ".selector" ).accordion({ active: <?php echo(isset($_GET['active']?$_GET['active']:"1")); ?> });