In Facebook's case, though—see above—there were two final rejections. A final rejection happens when all the claims are invalidated, so your submission is now vacuous.
It's called an IPR, an inter partes review [0] in the USPTO. Most potential challengers, though, are likely to save their ammunition for if and when they get sued on the patent. (And they might quietly let Facebook know they have prior art, so as to discourage FB from getting aggressive — FB might want its patent to remain officially valid, so as to be able to continue to rattle its saber at others, instead of having invalidity officially confirmed.)
[0] https://www.wikiwand.com/en/Inter_partes_review
It's called an IPR
Obligatory warning: I'm not a patent lawyer but I've responded to both final and non-final office actions, eventually getting a patent