I switched phones, and I also discovered a setting I previously disabled had restored back to default. I won’t elaborate on why you may not want videos in the Facebook app to start playing automatically, but here again, is how you shut it down:
In your phone’s Facebook app tap the overflow menu
Scroll down and tap App Settings
Once there, scroll down and tap Autoplay.
You will notice mine was already set where I want when I took this screenshot, but if you have a new app install yours will probably be set to On Mobile Data and WiFi Connections. You can choose whichever option you wish, I just prefer to use WiFi Only.
That’s it. Now your device’s mobile data won’t take a huge hit, meaning your wallet won’t either. Also, since Facebook likes to change settings for no reason, this might be something to check now and then.