S&P was down a lot too. Just one of an infinite number of reasons to not assume price action on a company can be traced back to a given news story.
My investment account seems to disagree too. The stock was down more than $1 before the market even opened based on that sham study by Princeton.
Why are you so sure that was the cause of the price decline?
The other big news was that Facebook was testing ads outside of their own platform. The possibility of taking on Google's Adwords and adding more than a few billion dollars in revenue should have increased the price?
You're layering a lot of your believe about Facebook onto that assumption - maybe people saw that news and concluded Facebook would fail in external ads and lose a bunch of money, which decreased the stock price. It's hardly unambiguously good news (like record profits or something).
Irony overload. What was wrong with that paper again? Correlation != causation?
Pretty much every stock was down yesterday.
In the short term, stocks on Wall Street are essentially a random walk.