In the last two years, Facebook.com traffic has fallen from 8.5 billion visits to 4.7 billion, SimilarWeb revealed on Wednesday. Meanwhile, YouTube’s traffic, which hit 4.5 billion visits in July, continues to surge and will soon top Facebook to become the second-most-popular website in the world behind Google. The world’s largest search company, Google had 15.2 billion visits last month, according to SimilarWeb data.

At first blush, that would sound like bad news for Facebook, which has been in the midst of controversy and trouble after privacy concerns and a stock price decline continue to affect the company. However, SimilarWeb said that the reason for Facebook’s decline has more to do with mobile success than anything else.

The researcher contends that many of Facebook’s users are turning to mobile apps instead of the browser to access the social network. In fact, Facebook app usage is growing and total engagement on the world’s largest social network is up.

Meanwhile, Facebook’s other platforms, including Instagram and Messenger, continue to grow and help bolster the company’s broader appeal. Instagram’s Android users, for instance, are now in the app 56 minutes each day, according to SimilarWeb. Last year, they were spending 27 minutes on the app.

Looking ahead, SimilarWeb argues that Facebook must be evaluated not on its own but as part of the broader Facebook “ecosystem” that includes Messenger and Instagram. The company, SimilarWeb argues, is focused on building its entire slate of services and not just its social network.

Still, SimilarWeb is predicting a “paradigm shift” in the world’s largest websites. In addition to YouTube capturing the second spot, SimilarWeb believes Amazon and its 2 billion monthly visits are primed to take the fourth spot from Yahoo.