This article explains why you may see a Secure Connection Failed or a Did Not Connect: Potential Security Issue error page and what you can do. If you see a Warning: Potential Security Risk Ahead error page, see the What do the security warning codes mean? article. To troubleshoot other error messages, see Websites don't load - troubleshoot and fix error messages.

Secure connection cannot be established When a website that requires a secure (https) connection tries to secure communication with your computer, Firefox cross-checks this attempt to make sure that the website certificate and the connection method are actually secure. If Firefox cannot establish a secure connection, it will display an error page. Secure Connection Failed A Secure Connection Failed error page will include a description of the error, an option to report the error to Mozilla and a Try Againbutton. There is no option to add a security exception to bypass this type of error. The error page will also include the following information: 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. Did Not Connect: Potential Security Issue Certain secure connection failures will result in a Did Not Connect: Potential Security Issue error page.

Website issues TLS version unsupported Some websites try using outdated (no longer secure) Transport Layer Security (TLS) mechanisms in an attempt to secure your connection. Firefox protects you by preventing navigation to such sites if there is a problem in securely establishing a connection. Contact the owners of the website and ask them to update their TLS version to a version that is still current and still secure. The following change has been reverted for an undetermined amount of time, to better enable access to critical government sites sharing COVID19 information: Starting in Firefox version 74, the minimum TLS version allowed by default is TLS 1.2. Websites that don't support TLS version 1.2 or higher will display a Secure Connection Failed error page with Error code: SSL_ERROR_UNSUPPORTED_VERSION and a message that This website might not support the TLS 1.2 protocol, which is the minimum version supported by Firefox. The error page may also include a button, Enable TLS 1.0 and 1.1that will allow you to override the minimum TLS requirement; however, Mozilla plans to remove this option and permanently disable TLS 1.0 and 1.1 in a future version of Firefox. For more information, see this Mozilla page.

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message

https://support.mozilla.org/en-US/kb/connection-untrusted-error-message

Websites don't load - troubleshoot and fix error messages

http://kb.mozillazine.org/Error_loading_websites

What do the security warning codes mean

Hi imagefact2014

If FredMcd's ideas don't work then:

First, I would try upgrading to 77.0.1

Second, try turning off DNS over HTTPS (DoH) (it seems like it fixed the problem for some folks in bug 1637512). You can disable DoH in your Firefox connection settings: using the following instructions which are from https://support.mozilla.org/en-US/kb/firefox-dns-over-https#w_manually-enabling-and-disabling-dns-over-https  :

1. about:preferences#general
2. In the {menu General} panel, scroll down to Network Settings and click the {button Settings…} button.
3. In the dialog box that opens, scroll down to Enable DNS over HTTPS.

   • Off: Deselect the Enable DNS over HTTPS checkbox turn it off

   

4. Click OK to save your changes and close the window.

Cheers!

...Roland