With the latest Facebook it appears that videos auto play again even if you had previously stopped them. 

This change is not only annoying but can quickly eat your cellular data, thankfully switching them off is easy. 

1. Head to settings and then account settings

 2. Videos & photos

  

3.   Select auto play
4. Now you can either select to play on wifi only or to never auto play. 

 
We hope you find it useful.