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.
This (recently introduced) Facebook feature that enables videos to start playing the minute you see them has caused a fair amount of consternation amongst its users.
Videos consume substantial amounts of mobile data. This is problematic for people that have limited data plans and spend a lot of time scrolling through the Facebook News Feed. Facebook enabled videos to automatically play by default, which has caused many people to incur high data usage charges.