Based on what I've heard, it was just a rumor. Originally it was just for laughs but then some people mistook that information and created a rumor out of it.
Totally an hearsay, I can't find any reliable source that tells facebook is starting to accept bitcoin very soon. 3 years after OP asked this question still no one gave a source that prove that Zuckerberg is considering bitcoin integrating to his business. But it will be a great adoption if he'll start to use bitcoin for facebook as it's now on the trend and bitcoin now is very popular.