Now Facebook has enabled autoplay of videos for all the users by default. It could be annoying for some people, even it could increase your data bills. You can very well disable this from your mobile itself.
Go to the More Tab, you will find the settings as shown above
Select the Account Settings, I initially thought this setting would be on the News Feed Preferences, but not, just go to the Account setting
Click on the Video and Photos
Now you can select never Auto Play, if you do not want this Auto Play feature. There are other options like On Mobile data and Wifi Connection and On Wifi Connection Only. In the same way , you can disable autoplay on your browser also.