I have Liberty plan 12. I don't watch movies online or download movies. I do have Facebook but don't leave it on all the time. When done on Facebook I shut it down. But there's different apps. Whatever I don't need and can shut down I do. You might have to check Facebook Settings. I do download small UTube files I also have the setting s at 360 or something like that or 460 I think it is. Anyway keep the number low. But so far I still have data at end of month so haven't been in Liberty Pass yet. Also there may be programs updating.
Facebook and other web sites have switched to using HTML5 for videos - depending on your browser's support for HTML5 media, they may be pre-loaded regardless of your intent to watch them or explicitly clicking to play them.