How do I configure Firefox to connect to my proxy server using HTTPS, not HTTP? If I enter "tls.example.com" as my HTTP proxy, and 443 as the port number, Firefox sends an unencrypted "CONNECT" header on port 443. Of course, this is wrong, because my proxy server only speaks HTTPS, not HTTP. If I enter "https://tls.example.com/" as my HTTP proxy, and 443 as the port number, Firefox says "Hmm. We’re having trouble finding that site." but in fact, Wireshark confirms that Firefox never even tries to connect to anything! It never sends a single SYN packet at all. According to: https://bugzilla.mozilla.org/show_bug.cgi?id=378637 Firefox does support the behavior described. That link doesn't explain how to configure it, though.