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When a website that requires a secure (HTTPS) connection tries to communicate 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 message, which usually means
- Firefox can’t verify the site’s security certificate, or
- Something on your computer or network is blocking or replacing the secure connection.
This article explains why you may see a Secure Connection Failed page or other connection security error and what you can do about it.
Table of Contents
Secure Connection Failed
A Secure Connection Failed error page will include a description of the error and a button. 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.
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Some websites try using outdated (no longer secure) Transport Layer Security (TLS) mechanisms in an attempt to secure your connection.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 secure.
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 a SSL_ERROR_UNSUPPORTED_VERSION error code and a message that says: This website might not support the TLS 1.2 protocol, which is the minimum version supported by Firefox. For more information, see this Mozilla blog post and Transport Layer Security (MDN Web Docs).
Did Not Connect: Potential Security Issue
Certain secure connection failures will result in a Did Not Connect: Potential Security Issue error page.
The error page will include a description of the potential security threat and an button to view the error code and other technical details. There is no option to add a security exception to visit the website.
HSTS required
Websites may require HTTP Strict Transport Security (HSTS) and will not allow access with an insecure connection.
Warning: Potential Security Risk Ahead
Firefox checks a website’s security certificate to ensure the site is legitimate and that your connection is encrypted. If the certificate can’t be validated, Firefox will stop the connection and display a Warning: Potential Security Risk Ahead page.
Click the button to view the error code and additional information. Depending on the error, you may be able to bypass the warning and visit the site. To learn more, see What do the security warning codes mean?.
This error can be caused security software products that intercept secure connections by default, which can produce connection errors or warnings on secure websites. For more information, see Troubleshoot security error codes on secure websites.
An incorrect system clock can also cause Firefox to detect that the website's security certificate is expired or invalid. Make sure your computer is set to the correct date, time and time zone. See Troubleshoot time-related errors on secure websites.
Other possible solutions
- Check if the website is down: If a website won’t load in Firefox, it might be a problem on the site’s end.
- Try opening the same site in another browser: If it doesn’t load there either, the website is likely experiencing issues.
- Clear cached certificates in Firefox: If Firefox has saved an outdated or untrusted certificate, removing it may fix the error. In the Menu bar at the top of the screen, click and then select or , depending on your macOS version.Click the menu button
and select .
Go to the panel, go down to the Certificates section, click , select any untrusted or outdated site certificates and click .
