session codeigniter localhost
The library you are using is external to the core CodeIgniter codebase and therefore isn't able to communicate with native functions in the normal way; instead of using $this as your reference to the CodeIgniter instance, in your library you should be using $this->ci so to access session data, your code would look something like:
$this->ci->session->userdata();This is explained in more detail in the CodeIgniter documentation here
in the view use $this->facebook->session instead of $this->session and it will work ;)