How do I turn off auto-playing videos on Facebook?
Version 6.8 of Facebook adds auto-playing videos to your news feed. The good news is videos don’t automatically play sound, but the bad news is there is no way to turn off the new feature when you're connected to a Wi-Fi network. Luckily, there is an option to disable them while you are on a cellular network so you do not burn through your data plan. Here's how:
Navigate to your Settings app > Facebook > Settings and tap the slider that reads "Auto-play on WiFi only". This will disable the auto-playing videos in your news feed when you're connected to a cellular network.