It would appear that Facebook doesn't know when to stop. First they purchase Instagram, then they bought patents from Microsoft, then, of course, the disaster that was their IPO. With a pending lawsuit for misrepresenting growth rates and revenue, now would probably be the worst time to make a large purchase.
On the other hand, Facebook is seemingly run by a bunch of chimps, so logic doesn't factor into their decisions. Their current area of interest is in picking up a web browser. Considering the pending lawsuits include accusations about a rise in mobile browser and app-based users, neither of which Facebook is able to capitalize on, it does make some sense that they would be interested in teaming with or purchasing a browser company. Internet Explorer is out, for obvious reasons, and Chrome and Safari are both owned by companies they consider competition, so the only option left is Opera Software.
While Opera might not be a leader in the industry, or even a name more people know, it has markets in which it is strong.