To add photos to Arkiver from your Facebook account, you'll need to connect to Facebook.
1) Click "Connect to Facebook" in the Moment Uploader screen
2) If you're currently logged into Facebook it should automatically connect you, otherwise you'll need to log in to Facebook in the window that appears.
3) That's it! You'll be connected and all your Facebook albums will appear and you can navigate through them and pick photos to upload to your Arkiver. Once you've connected, you won't have to go through this process again. Hooray!