However, if you want to make things easy on yourself and disable Autoplay period, for everything -- whether with a cellular or WiFi connection -- you can now do so. And it's very easy.
For Apple iOS devices, you can make your selection under Settings/Facebook. For Android, it's found in Settings for the Facebook app. As you can see below, you'll be given the choice of disabling Autoplay so that it runs only when you're connected to WiFi or disable it entirely.