I know of a very popular newswebsite in my region which somehow works around this: When overscrolling the video window on their site, ALWAYS the video starts to play - I have the option disabled in FF settings, nontheless its not working in this case :-X

That’s interesting. I guess Firefox is taking the scrolling as user interaction, allowing the video to play. There’s a chance Firefox would fix this, if reported.

I'd just disable js entirely for that site. And if it breaks it entirely, oh well