"You can now also comment on stories you see when you don't have an internet connection. While the ability to like and share posts when you're offline has been available for some time, now you can comment on posts and the comment will be posted whenever you next have a connection.Continuing to build News Feed for all types of connections | Engineering Blog | Facebook Code
For example, if you see a post about a friend's engagement when you're not connected to the internet, you can compose a congratulatory comment, and it will appear on his or her post when you're back online.
These changes will help anyone who is on a poor internet connection — even those whose network connectivity is generally good but who have intermittent connections in places like subways and tunnels, or at large events. None of these changes affect News Feed ranking. We are simply showing you the most relevant content as efficiently as possible. We'll be testing and rolling this out over time to gather feedback."
Thursday, December 10, 2015
Continuing to build News Feed for all types of connections | Engineering Blog | Facebook Code
Check the full post for more details on stories via slow connections