Facebook's traffic hasn't just fallen by about half since 2016, according to the study. Among the consequences of such a precipitous drop is the opening it's given to YouTube, which the study's data shows is about to overtake Facebook to become the second biggest site, traffic-wise, in the U.S. Which would give Google ownership of the top two spots, pushing Facebook down to number three.

CNBC describes the drop at Facebook as "severe" and goes on to round out its list this way: "The five websites receiving the most traffic in the U.S. in the last several years have been Google, Facebook, YouTube, Yahoo and Amazon, in that order. However, Facebook has seen a severe decline in monthly page visits, from 8.5 billion to 4.7 billion in the last two years, according to the study. Although Facebook's app traffic has grown, it is not enough to make up for that loss, the study said."

Google trouncing Facebook is a bit ironic, considering it was Google's attempt at a feed-based social network (Google+) that ended up falling flat, when it turned out Google already owned a social winner this whole time in the form of YouTube.