If I read the thread so far correctly, you are in a position that you have added DNS blackholes for facebook.com and google.com, but are unhappy that the domain fbcdn.net and traffic to facebook's IP space are not blocked when you expected them to be.
The behaviour you're seeing is correct for the configuration you have so far, if you want other domains blocked (like fbcdn.net) then you need to block them in your list as you have done for the other domains. Many other domains for both facebook and google will also not be blocked (for example youtube.com even though it is part of google).
Even when you block the DNS request pfSense will not stop traffic going to IP addresses directly (for example pinging 31.13.70.7 would still work). To block traffic entirely you would need to add their domain/AS numbers to IP4 & IP6 lists (Google are AS15169 and facebook are AS32934) and tick the 'domain/AS' box. I can't remember if you need to include AS prefix as part of the number or not, I'm sure someone will be able to confirm that for you.