Hope you have noticed the new feature in Facebook which autoplays all the videos that are shared with you. This feature is ON by default on web and Mobile applications.
This feature (I will call it as Bug), will download all the videos, even if you have facebook.com just opened in a tab of your browser or you have the Application installed on your Phone, and will consume a loads of bandwidth of your Mobile data / WiFi.
To save your Mobile / WiFi Data Usage bills, Make sure it is Turned OFF, This will load the videos when you need by clicking it as before.
How to Disable Auto-Play
Facebook.com on a desktop or laptop – Go to Settings using the drop down menu > click Videos > Click on the drop-down menu next to “Auto-Play Videos” and select Off.
Android – Open Facebook Application >> Hit Menu Key >> Settings >> Video Auto Play >> Set it “Off“
iOS – Go to the Settings app > Facebook > Settings > Auto-play > set to “Off”