As the past of being white hacker shows, keep hacking but shut up! Because even if you tell the author you find a way to get into their system and you havent cause any damage, they sure will come after you in a legal way.
In example herein, not only time after time the author proves that there are serious holes in FB auth system, but is also very happy to blog about it. You see, FB is publicly traded company. The management answers to stockholders and the board. If some Joe Hacker keeps finding holes in the system, someone somewhere reading that blog may be thinking of abandoning the FB platform due to it security layer looking like a swiss cheese. And management doesnt like that, because less users == less eyeballs for $.
My gut tells me, if this guy did not get offer to work for Facebook just yet, it means they are building a lawsuit against him, as you perfectly know FB TOS forbids anyone from fiddling with any of their URLs.