This uses the hooks system and tabbed display of admin / orders implemented by the Paypal App.
It adds a tab to admin / orders which lists all orders from the customer of the current order. The current order is highlighted. Clicking on one of the other orders will load it instead. Works for all orders, not just those paid by Paypal.
COMPATIBILITY Compatible with the tabbed admin orders page of the Paypal App in any version of osCommerce (2.2RC2, 2.3.x). FILENAMES DEPRECATED - if your admin / orders page is not called orders.php you'll have to change the hard-coded name in the module. Not compatible with BS EDGE Hooks of 2016-10-03 (which don't cover admin).
Uses tradition language defines, not Paypal App-style.
INSTALLATION Just copy the 3 files to your store. No code changes and no admin install - it just works.
from the addons area http://addons.oscommerce.com/info/9511
GITHUB also available in a branch on its own in a fork of gburton/Responsive-osCommerce at: https://github.com/BrockleyJohn/Responsive-osCommerce/tree/addon_customer_orders_tab