Websites still find their way around this setting. I think they put an overlay on the page and intercept the first mouse event they can, and use that to start playing the video.

I usually just blacklist these websites in my Pihole.

There's an old add-on, Disable HTML5 Autoplay, that still works most of the time and can whitelist sites.

https://addons.mozilla.org/en-US/firefox/addon/disable-autop...