FB gobbles up your data budget if you look at the News Feed, or other autoplay web sites. You can stop this by modifying smartphone settings.
Smartphones have options to play videos automatically when connected to Wi-Fi only. Here are instructions for turning off the video auto-playing feature using Facebook for an example:
Android
Settings > App Settings > General Settings > set Auto-play to “Wi-fi only” or “Off”
iOS
Settings app > Facebook > Settings > Auto-play > set to “Wi-fi only” or “Off”
Desktop or laptop
Settings using the drop down menu > click Videos > Click on the drop-down menu next to “Auto-Play Videos” and select Off.