I use Mozilla Firefox and have never experienced that. It's a bit seldom to find websites not automatically redirecting to https:// though. You can try http://repo.mysql.com/ . Sure, the browser has that icon in the URL bar saying that the connection is unsecure. It does also show a big warning, if something with the certificate is wrong and enforces HSTS (which I don't like). But an unencrypted connection works just fine.
I'm not using other browsers often, so I my perception is maybe skewed, but I wouldn't have expected them to block http and if I would see that, I would perceive that as a bug.
