I don't know what happened, but it feels like since Firefox 65 came out, YouTube videos no longer play on here. When I click on one of the placeholders for a video, it just disappears and leaves a blank space where the placeholder was. I've tried turning off adblock and NoScript with no change.
I posted about this on /r/firefox/ and somebody said that
"Browser console shows:
Blocked loading mixed active content “http://www.youtube.com/embed/MWxlbnI9mpU?autoplay=1”
Linking to https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content
Tell the forum to update their embed code to load the https version of YouTube.
It doesn't work for me in Firefox 60, 63 or 64, FWIW (via mozregression)."
Someone else said that it works in IE, but not Firefox, so something likely changed in Firefox recently to cause this.