I don't know if this is a site problem or a Firefox problem, but it is a little something that I've noticed for quite a while now...
The following screenshots show the problem occurring on a random post in recent discussions:
Broken avatar using Firefox 65.0:
Correct avatar using Chrome 72:
If someone's avatar is broken, it is broken everywhere it is displayed. I honestly have an inclination that it is just Firefox bugging out, and not the site, but I thought I should report anyway to get it cleared up.
All other browsers I've tested render the avatars correctly, but of course I'm that one irritating person that prefers using Firefox over everything else