Looks like the favicon got corrupted somewhere along the way (it did exist, but it was 0 bytes). I re-uploaded it and it should hopefully work normally for everyone again. Guess it was just cached for everyone who still saw it?
We don't force HTTPS because it was causing issues for one of our team members. We are using Let's Encrypt (
https://letsencrypt.org/), which needs some kind of modification to the browsers (not supported universally, but well supported in recent browsers).