Yes, the q2a field contained an URL different from the URL that I had inserted on the facebook app. About the URL that I use to navigate on the q2a installation on my pc, I''m using a "virtual" URL (www.question2answer.com) that , in the Windows HOST file (Windows/system32/etc/drivers) , i've remapped to a local IP that I have on my pc. I've inserted this URL in the facebook app and in the q2a "preferred site Url" field, and now I can authenticate with any facebook account on the q2a installation that I have on my pc and I''m using for testing.