I was going to rant something about open standards and how they did not care to test this toy on Firefox (but they did it test it on safari), but I grew tired.
According to MDN, the feature can be enabled in Firefox by enabling layout.css.scroll-driven-animations.enabled in Firefox (though the demos don't work, looks like there are still some implementation bugs). I don't really mind proof of concept demos like these only working in some browsers. The feature is still useless on real websites, but who cares about a silly cat GIF made up of CSS boxes not working.
The last one even works on Firefox for Android, and most of the manually scrolling ones do too