CI_Facebook is a Facebook Library for CodeIgniter.
Simply copy/merge all the files into the corresponding locations and setup config/facebook.php.
There are unit tests written for each function/class. You will need PHPUnit to execute them.
Accessing the Facebook object is easy since the hook is auto-loading it.
e.g. $user_data = $this->facebook->fb->api_client->fql_query("select name from user where uid = TARGETUSERID");