Facebook seems to be planning for some serious long-term growth. Last night, Menlo Park officials gave Facebook the go-ahead to expand its headquarters enough to accommodate 6,600 workers. That's triple the 2,200 workers based at the facility today, and almost double the current ceiling of 3,600. That's not it for growth plans, though. The company wants to occupy another campus across the street that would allow it to house up to 9,400 people. The deals aren't done, however. Atherton, the city next door to Menlo Park, still has concerns about traffic and won't sign off until they're addressed.