Hi Tor,
Facebook restricted their API about a year ago and now you will only be able to see friends who accepted the Wolfram app that connects the WL with Facebook API.
For example, in my case, from my total amount of friends I only get 17. It's not a coincidence that those friends I can see are Wolfram employees or Summer School students who, in some point, accepted the app when testing SocialMediaData or probably W|A Facebook Analytics.
I hope that helps.