Firefox gives:

Secure Connection Failed

An error occurred during a connection to my-ssl-site. SSL peer reports incorrect Message Authentication Code. Error code: SSL_ERROR_BAD_MAC_ALERT

  • The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
  • Please contact the website owners to inform them of this problem.

But does not give an option to proceed anyway.

  • Note that MAC in this context is "Message Authentication Code", not one of the other plethora of computing uses for the acronym "MAC". The specific MAC algorithms are selected based on the negotiated Type (stream, block), Cipher Family (SSLv2/3, TLSv1.0/1.1/1.2), Mode (CBC, GCM, CCM) and, Hash Algorithm (SHA1/128/256/384/512) for the connection. If the server and client don't both support/allow a set of common families/modes/hashes, or if there are incompatibilities in the algorithms, a message like this would be displayed. – Frank Thomas Dec 27 '17 at 0:05

Go to about:config. Add my-ssl-site to security.tls.insecure_fallback_hosts:

security.tls.insecure_fallback_hosts my-ssl-site

Seems to be broken in Firefox 80.0.

| improve this answer | |
  • Now fails for many sites reached from start.att.net, and for returning to start.att.net. The browser I use is Mozilla Firefox Quantum 69.0 (64-bit). Clicking on Retry usually makes it work, but not always. – milesrf Sep 8 '19 at 2:35
  • 1
    Of all the answers found on the internet, this is the one that actually worked. And it even is way better, as it only allows this insecure way to work for specific sites only. In my case, I am using an old printer with its own website, using a self-signed certificate. Apparently, Firefox didn't like the old school style of it... – Akito Apr 5 at 9:55
  • 1
    @Akito Guess why I had the problem :) – Ole Tange Apr 5 at 18:18

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