It's best to answer this question by indicating you're hoping for career growth within the company. Avoid saying this is just a "stepping-stone" or a temporary position while you're moving toward goals that will take you in another direction.

"I'm not sure I have it all figured out yet, but I do know I'd like to grow into a management role with Facebook. I love learning and have a strong background in leading teams, so I'm hoping that once I establish myself here, there will be opportunities for improvement."