https://support.mozilla.org/en-US/kb/content-blocking

I'm liking strict mode, especially the fact that it blocks embedded social media stuff, which uBlock Origin doesn't do (by default).

Somewhat related, if you want to prevent videos from playing automatically go to about:config and change the "media.autoplay.allow-muted" to "false".
I'm guessing Satan and his league of web developers complained about the outright blocking option.
"Could you let the video play as long as it's muted? I mean our goal is just to waste people's bandwidth, it's not really about the content anyhow."


Code:
// Whether to autostart a media element with an |autoplay| attribute.
// ALLOWED=0, BLOCKED=1, defined in dom/media/Autoplay.idl
pref("media.autoplay.default", 0);
Code:
// By default, don't block muted media from playing automatically.
pref("media.autoplay.allow-muted", true);
https://dxr.mozilla.org/mozilla-rele...ef/init/all.js