Disable HTTPS upgrade?

The release notes say:

> Firefox now upgrades page loads to HTTPS by default and gracefully falls back to HTTP if the secure connection fails. This behavior is known as HTTPS-First.

The HTTPS-First doc says: https://support.mozilla.org/en-US/kb/https-first

> Some websites only support HTTP and the connection cannot be upgraded. If an HTTPS version of a site is not available, the site will load but through the less secure HTTP protocol. In some cases, websites seem to support HTTPS but serve different content from the HTTP version or behave different in other ways. To avoid upgrade attempts users can enter an address in the address bar with an explicit http:// scheme. Permanent exceptions added in the HTTPS-Only Mode section in Firefox settings will also prevent upgrades.