Bug1038424

Because that's what the HSTS solution proposed on comment 2 does, it silently upgrades to the secure version of the protocol. If the secure protocol isn't supported by the server it will fail in any case
Also, because this isn't something that the user can directly fix, so it doesn't really makes much sense informing him that the configured server is http and that he should modify it to https. This way, if the server is configured as HTTP but the HTTPS server is also up, it will simply work