It has been discussed here before, but I just want to point out that this follows you across topics in the forum if you happen to sroll past a post where someone has attached Youtube content:
Right. Or you can set NoScript to allow no scripts to run until you specifically authorize them, as I do.
But that doesn’t help forum members who aren’t running NoScript or another blocking extension. The question is how to prevent Discourse from silently connecting to external sites when a onebox link is posted here.
For a privacy-focused site like Purism’s community forum it’s just bad behavior (although it’s Discourse’s “fault”).