Read the error code first. Then: correct the date and time, set Firefox to No proxy, pause antivirus HTTPS scanning, and test in Troubleshoot Mode. If only one site fails on every device, the site's certificate or HTTPS setup is broken.

The short explanation

“Secure Connection Failed” is the headline for several TLS problems. Errors that affect every site point to your computer (proxy, antivirus, clock). Errors on a single site point to that site’s server.

What you'll see

  • “Secure Connection Failed” with an error code.
  • “The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.”

What causes it

  • Wrong system clock.
  • Proxy, VPN or antivirus interception.
  • Modified Firefox security settings.
  • Server TLS misconfiguration.

How to fix it

  1. Note the error codeUse it to pick the matching guide (PR_END_OF_FILE_ERROR, SSL_ERROR_RX_RECORD_TOO_LONG, etc.).
  2. Fix date and timeEnable automatic time sync in your OS.
  3. Proxy settingsFirefox → Settings → Network Settings → No proxy (or system proxy).
  4. Antivirus HTTPS scanningPause it and retry; add an exception if that fixes it.
  5. Troubleshoot ModeHelp → Troubleshoot Mode to rule out add-ons; refresh Firefox from about:support if needed.
How to tell it worked: Sites open with the padlock and no warning.

Stop it happening again

Avoid HTTPS-intercepting tools and keep Firefox up to date.