Facebook’s own official Windows 10 app has been available for the desktop for some weeks now. The app is now however officially available for Windows 10 Mobile, at least in some regions.
If you change your region to France you can now download the full-featured app. If you have Facebook’s new W10 app installed on your desktop you can also access it via your Library list found in the Store app.
See screen shots of the app below:
Find the app in the Windows Store here.