Here's how to find out: Set up a page on a server you control that has a URL you know that Facebook has never seen. Start making a posted item on Facebook wit

Here's how to find out: Set up a page on a server you control that has a URL you know that Facebook has never seen. Start making a posted item on Facebook with that URL. Check your logs and see what User-Agent Facebook is using, and try to get your best guess as to what is going on. Beyond the User-Agent (which might just be something like "Facebook") you could always dive deeper by investigating the actual packets sent and comparing them to those generated by something like wget or cURL.