AddressBookSync is a simple application that synchronizes user photos on Facebook with the records in your Mac Address Book. In order to do this, the app requires access to your Facebook account via FacebookAuth.
Note that no URL bar is present, nor is it indicated that the connection is secure.
Furthermore, Facebook even provides the notice on their sign in form: Security Note: After login, you should never provide your password to an outside application.
If you close the Login Sheet before successfully authenticating, you are given this error: