<h1>Thank You, 
<?php
$node = node_load(arg(2));
$node_language = ($node->language) ? $node->language : LANGUAGE_NONE;
if (isset($node->field_donation_customer_data[$node_language][0]['value'])) {
  $customer_data = unserialize(aes_decrypt($node->field_donation_customer_data[$node_language][0]['value']));
  if (isset($customer_data['firstname'])) echo ' ' . ucfirst($customer_data['firstname']);
}
?>
!</h1>