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, or
• The problem is with the website.

Firefox blocks these connections to help protect your personal information.

This article explains why you may see these warning pages, whether you can safely continue, and what steps you can take to resolve the problem.

Identify the error page

First, use the error page in Firefox to understand what to look for next.

Secure Connection Failed

SSL_ERROR_UNSUPPORTED_VERSION

Error code SSL_ERROR_UNSUPPORTED_VERSION means the website uses an outdated version of Transport Layer Security (TLS).

Firefox blocks the connection because the TLS version is no longer considered secure.

You can't fix this problem in Firefox. Contact the website owner and ask them to update their server to a supported TLS version.

For more information, see this Mozilla blog post and Transport Layer Security (MDN Web Docs).

Other Secure Connection Failed errors

Other errors, such as SSL_ERROR_RX_RECORD_TOO_LONG or PR_END_OF_FILE_ERROR, can occur when another feature, program or device interferes with encrypted connections.

Common causes include:

• VPN software
• DNS over HTTPS
• Antivirus software that scans encrypted traffic
• Firefox connection settings that may include proxy servers
• Network security appliances or firewalls
• Enterprise or school network security software

Continue to the Possible solutions section below to troubleshoot these causes.

Did Not Connect: Potential Security IssueBe careful. Something doesn’t look right.

Some websites use HTTP Strict Transport Security (HSTS), which requires a secure connection every time you visit.

When a site uses HSTS, Firefox won't let you bypass the warning. This protects you from attackers who may be trying to intercept your connection.

If no "Proceed" button is available, you'll need to resolve the underlying problem before you can access the site.

Other Security Risk warnings

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 error page.Warning: Security Risk error page with the message, Be careful. Something doesn't look right.

Click the Advanced…Advanced button to view the error code and additional information. Depending on the type of error, you may be able to bypass the warning and visit the site by clicking Accept the Risk and Continue.Proceed to <website> (Risky).

Other Warning: Potential Security Risk AheadWarning: Security Risk errors cannot be bypassed and can be caused by security software or networking tools that intercept secure connections by default.

To learn more, see What do the security warning codes mean? and Troubleshoot security error codes on secure websites.

Possible solutions

The steps below address the most common causes of secure connection errors. Try the suggestions that best match your situation.

If the problem started after you installed or updated security software:

Some antivirus programs inspect encrypted connections and can interfere with Firefox.

• Update your antivirus software to the latest version.
• If the problem continues, review and/or modify your antivirus settings for HTTPS or encrypted connection scanning.

If you're using a VPN:

VPN software can sometimes prevent Firefox from establishing a secure connection.

• Temporarily disable your VPN for the affected website.
• If you're using Mozilla VPN, see Disable Mozilla VPN protection for a specific website and Troubleshoot Mozilla VPN connection problems.

If you're using a proxy server or custom network settings:

Incorrect proxy or network settings can prevent secure connections.

• Check your Firefox connection settings to see whether a proxy is configured.
• If you're using DNS over HTTPS, temporarily disable it it or add the affected website to the Exceptions list. See Configure DNS over HTTPS protection levels in Firefox.

If your computer's date or time is incorrect:

An incorrect system clock can cause Firefox to treat a website's certificate as expired or invalid.

• Verify that your computer's date, time, and time zone are correct.
• See Troubleshoot time-related errors on secure websites.

If the problem is with the website:

Sometimes the issue is on the website's end rather than your device.

• Check whether the website is down.
• Try opening the site in another browser. If it doesn't load there either, the website is likely experiencing an issue.

If Firefox has saved an outdated certificate:

Firefox may have cached an outdated or untrusted certificate.

1. In the Menu bar at the top of the screen, click Firefox and select Settings (or Preferences, in some cases).Click the menu button and select Settings.
2. Select Privacy & SecurityPrivacy and security.
3. Scroll to the Certificates sectionConnection and software security section, click Advanced settings and go down to the Certificates section.
4. Click View Certificates…Manage certificates.
5. Select the outdated or untrusted certificate and click Delete or distrust….

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