Of all the popular social media companies out there, Facebook always feels like the most troubled. It also has more users than any of its competitors, so criticism is easy to come by. Ever since it's lackluster IPO, the company has been scrambling to come up with a way to reassure investors that they are worth the billions they were valued at. Responding to market pressures, Facebook has aggressively pushed the message that they are focusing their energy on becoming a mobile service first and foremost. As more and more users access the internet primarily through their phones, Facebook is rushing to change the way they operate in order to meet the needs of changing demographics.
They've restructured their staff, requiring all of their developers to have skills in mobile application development. Whereas previously the company had a small, dedicated staff that worked exclusively on mobile, now mobile is factored into every project. For example, the team which develops the Messenger service (you know, the Facebook instant messaging feature that is both really useful and often infuriating?) also has to develop for the mobile app version of Messenger at every step of the way.
The most important thing Facebook needs to tackle first is getting its mobile app working properly. If you own an iPhone, you've no doubt noticed the constant updates that keep coming out. As of late, they've all been for the better! Hopefully with time they can get the app moving fast enough that it's always an enjoyable experience.