Facebook object of any webpage can be obtained by using the graph api from the url https://graph.facebook.com/?id=[url of the page]

For example  https://graph.facebook.com/?id=http://anilmaharjan.com.np/blog/2012/05/facebook-object-id-from-url-of-webpage for this page.

You can get the facebook object of thread of comments on this page  here https://graph.facebook.com/comments?id=http://anilmaharjan.com.np/blog/2012/05/facebook-object-id-from-url-of-webpage

You can use other arguments as your requirements.