Migrate from HTTPS-Everywhere to FIrefox's own HTTPS-First feature

Firefox exposes the prefs dom.security.https_first and dom.security.https_only. The former attempts to default to HTTPS when no protocol is specified; the latter forces all connections to HTTPS and displays a warning if this causes a failure. The warning looks similar to the warning for expired TLS certs, and allows users to bypass it.

Firefox also has dom.security.https_only_mode.upgrade_onion to allow an exception for all hidden services.

Using these facilities could eliminate the need for the HTTPS-Everywhere addon, keeping the Tor Browser's addon list smaller.