This is known as peek and pop, and was introduced as part of 3D Touch on the iPhone 6S and 6S Plus last September. The display on both of those phones has pressure-sensing capabilities allowing the phones to detect how hard you are pressing.
Apple added these features to its own apps at that time, but other developers are finally starting to see the merits of this new interaction. Apps like Instagram, Flickr, and Dropbox have added 3D-Touch capabilities.
The current Facebook app already has 3D-Touch controls, but they are limited to the app icon from the main home screen. You can hard press on the icon to open a popup that lets you choose what action you want to take. For example, you can choose Take Photo/Video, Upload Photo/Video, or Write Post. This is a lot quicker than tapping the icon to open the app, followed by finding the desired function.
By adding peek and pop to the timeline, users should find navigating to be more efficient.
Facebook is currently testing this new feature with a “small group,” and a wider roll-out is expected in the coming months.
