Nothing is more infuriating that going to a website with a video playing on the background. That is what Facebook is exactly doing. They are now playing videos on pages that you open. Sounds like they are more concerned more about counting their video views than the actual user experience. At least they’re trying to be nice by muting the audio if you scroll down past the video. Facebook is giving you the option to have the volume ON automatically, but why would you do that? If you don’t want videos playing in the background at all, you can turn it OFF by going to the Settings and setting Auto-Play Videos to Off. That’s what I would do.
Facebook Video Auto Play