Some users have avatars that won't show up, for example,
Consistently across the whole site, for example, in chat oneboxes:

Inspection of the profile page tells me this is with Facebook avatars.

My browser refuses to load this shit for security reasons:

I've seen this behaviour for a while now. It might be due the fact that I don't facebook, or perhaps it is in the aftermath of Heartbleed?
This reminds me somewhat of the situation we had back when OSCP verification was introduced (Firefox/Opera stops showing Gravatars linked over https), but it doesn't seem to be the same issue, and limited to Facebook's servers.