Mixed content occurs when initial HTML is loaded over a secure HTTPS connection, but other resources are loaded over an insecure HTTP connection.| web.dev
Most of the web already supports HTTPS: In fact, 93% of requests made by Firefox are already HTTPS. As a reminder, HTTP over TLS (HTTPS) fixes the security shortcoming of HTTP ...| Mozilla Security Blog
InfraUnicode and Encoding| html.spec.whatwg.org