I'm Seamus Byrne from CNET with a quick tip on saving mobile data.
Have you noticed that when you're using your Facebook app, that videos start playing automatically when they scroll onto the screen?
That's using data.
Here's how you switch that off so that they won't autoplay when you're using your mobile network.
Go to More.
Then Account Settings.
Then Videos and Photos.
And then change Auto-play to Use Wi-Fi Only.