Very cool:

FB writes,

[Y]ou just take a photo in Portrait mode using your compatible dual-lens smartphone, then share as a 3D photo on Facebook where you can scroll, pan and tilt to see the photo in realistic 3D… Everyone will be able to see 3D photos in News Feed and VR today, while the ability to create and share 3D photos begins to roll out today and will be available to everyone in the coming weeks.

Check out their post for tips on composing a 3D-friendly image (e.g. include lots of foreground/background separation; avoid transparent objects like drinking glasses).