In Firefox 83, Mozilla introduced a new security feature called HTTPS-Only Mode.
According to Mozilla, “the web contains millions of legacy HTTP links that point to insecure versions of websites. When you click on such a link, browsers traditionally connect to the website using the insecure HTTP protocol.”
With HTTPS-Only Mode enabled, Firefox will attempt to establish HTTPS connections to every website and will ask for permission before connecting to a site that doesn’t support secure connections. Even if you click on an HTTP link or manually enter an HTTP address, Firefox will use HTTPS instead.
Mozilla says, once HTTPS becomes even more widely supported, it will be possible “to deprecate HTTP connections and require HTTPS for all websites.”