Past info such as friends renamed or deleted cannot be retrieved: we start to track changes from your friend list after your first sign in on steamfriends.info. Remember that your profile and your friend list must be public.
Steamfriends.info uses Steam's official OpenID interface to authenticate your Steam account. In this process you sign in with your username and password on the Steam servers, after that the Steam server tells us if you logged in successfully and returns your 64bit Steam ID. Your user credentials will not be shared.