Many people have noticed that Facebook for iOS now has a great new "feature": auto play of videos. Videos posted by friends in your timeline will automatically start playing silently (for now) inline in your News Feed. Tapping on the video will bring it full screen with audio. While this feature can be useful for some, it can be a real data hog for others. If you're in a place with a slow connection, or using your cellular data plan, this can cause trouble. As of right now Facebook has only given us the option to disable while on cellular data, but not all together. Unfortunately when I'm flying and using airplane Wi-Fi this will be a huge bottle neck for me.
To disable, tap the Settings icon from your device's home screen. Scroll down to Facebook and tap on it. Then enter the Settings menu and turn on the "Auto-play videos on WiFi only" option.