Good luck. Facebook will be wanting to hear from you, because you're using their TM. Maybe, you will learn and hopefully not do it again.
If you dont make money from the site and it 'improves' user experience for facebook, go with it. But dont complain when they take the domain from you
Everyone goes crazy on copyright infringement. This would not hold up. U.S. Copyrights are very lenient when using words in the dictionary. This domain will be 100% safe as long as you stay away from a facebook themed website. Face, Book, and able are all English words.
I doubt that facebook would bother to do anything with this site, but If they want to take action, they will win the dispute. First of all, this is not a Copyright infrigement, it is Trademark infrigement, meaning, when you're trying to be smart, better do you homework first. Furthermore, facebook isn't a generic dictionary word. Even if it was, it wouldn't help, Apple has trademarked apple.com and Microsoft has trademarked live.com those are very generic everyday dictionary words. There've been numerous cases where individuals lost their domains containing apple or live from disputes from Microsoft and Apple respectively.
I would get it appraised and then sell it right away. Take the money you can for it if anyone is willing to purchase. I was thinking you could try to sell it to Facebook, Inc. but then they might put you on the hot seat. Good luck with it! Xinjiang