// get the "Admin" link's href
admin = document.evaluate("//a[.='Admin' and @class='admin']/@href", document, null, 2, null).stringValue;

// grab the script's ID from the Admin link's href
scriptID = ( admin.match(/\/(\d+)/) || [0, 0] )[1];

// quit if the admin link is not found
if(!admin || !scriptID) return;