I never knew this and thought it was worth sharing .....
Anyone noticed your data being used up quickly lately?
Well it is because facebook has changed your settings and as videos now auto play in your feed...that's huge data and costs you £.
On iPhone, go into your phone settings, go to FB icon, click on that, then on settings and select "auto play on wifi only".
On desktop go to the little triangle top right of your FB page, go to settings, down the bottom is videos, click on videos and move the slider to off
On android go into ap settings and do the same
On Samsung while in FB press the left button next to home key on the phone then press settings and it comes up with the auto play option.