Secure Connection Failed means Firefox could not complete a secure connection to the requested website. The error can involve the site's Transport Layer Security (TLS) setup, security software that inspects encrypted traffic, or a proxy between the browser and the site. The warning title alone does not identify the cause.

On a computer, start by reading the exact error code and checking whether other secure websites work. You may need to correct your device's clock, change a proxy setting, update software, or ask the site owner to repair the server.

Read the Exact Firefox Warning

Keep the address and the complete code shown on the error page. If the warning includes an Advanced button, open it for further details. Firefox displays several security warning pages, and their codes and available actions differ. Secure Connection Failed does not offer a security exception.

SSL_ERROR_UNSUPPORTED_VERSION points to a website using a TLS version Firefox no longer supports. The site owner must update that configuration. Codes such as SSL_ERROR_RX_RECORD_TOO_LONG and PR_END_OF_FILE_ERROR can involve a proxy, virtual private network (VPN), security product, or website configuration. If the code refers to the certificate's issuer or expiration date, check the certificate and your device's clock instead.

Compare Browsers, Devices, and Networks

Try a few other familiar HTTPS websites in Firefox. If several unrelated secure sites fail, inspect the device and its network first. If only one site fails, open it in another up-to-date browser. Even if the site opens in a second browser, a configuration problem may remain because browsers can use different trust settings or connection paths.

Try the affected site on another device and, if available, a different network that you trust. If the site fails to load in each test, the site itself is more likely to be the source of the problem. On public Wi-Fi, complete the network's normal sign-in process before testing again; contact the network operator if its sign-in page will not open. On a school or work connection, ask the administrator before changing a required proxy or security control.

Correct the Device Clock

Check the device's date, time, and time zone. A wrong clock can make a valid certificate appear expired or not yet valid. Correct the date and time in your system settings, then reload the affected page. On Windows 11, open Start, search for Date and time settings, check the time zone, and select Sync now.

This check is especially relevant when the error code refers to certificate dates. If the clock is already correct and only one website shows an expiration error, the owner may need to renew the site's certificate. Changing the clock to match an expired certificate would hide the actual problem.

Check the Proxy, VPN, and Secure DNS Settings

Open Firefox Settings. Depending on your version, look in General for Network Settings or Proxy settings. In versions with the newer layout, open Privacy and security, find Connection and software security, select Advanced settings, and then find Proxy settings. Select Settings or Configure proxy to open the connection options.

Record the selected proxy mode before making a change. If an unwanted manual proxy is configured on a personal network that requires no proxy, select No proxy and retry the site. Keep a required organizational proxy configured and ask your network administrator to correct any wrong proxy server address or port.

If you use a VPN, temporarily disconnect it and retry where network policy permits, then reconnect it. If the site opens with the VPN disconnected, the VPN's settings or the network path it uses may be involved, but that result does not identify the exact cause. Report that difference to the VPN provider or network administrator.

DNS over HTTPS encrypts the lookup used to find a website's IP address; it does not act as a VPN for the website connection. A different DNS resolver can return a different address. If the failure appears related to a custom secure DNS setting, find DNS over HTTPS under Privacy and security, opening Advanced settings if shown. Record the current protection level, briefly select Off and retry the site, then restore the original protection level.

Review Security Software

Some antivirus and network security products inspect encrypted connections and issue replacement certificates. If errors began after you installed or changed security software, or if they affect many sites, update that software and check its HTTPS inspection settings. On a managed device, ask the administrator to verify the required certificate setup. Do not import an unfamiliar certificate or permanently disable protection just to suppress the warning.

Update Firefox and Test a New Profile

For a desktop copy installed from Mozilla, open the application menu, then Help and About Firefox on Windows or Linux; on a Mac, choose Firefox and About Firefox from the menu bar. Install any offered update and select Restart to update Firefox when prompted. If Firefox came from the Microsoft Store or a Linux distribution's software repository, use that update service instead.

If the error persists only in Firefox after those checks, test the site with a new profile. Enter about:profiles in the address bar, choose Create a New Profile, and follow the setup wizard. Under the new profile, select Launch profile in new browser and retry the affected address before adding extensions or custom settings.

Creating a new profile makes Firefox use that profile by default, so return to about:profiles and choose Set as default profile for your original profile after the comparison. Keep the original profile and its data. If the new profile works, investigate the original profile's settings and extensions rather than assuming the server has been repaired.

When the Website Owner Needs to Act

For SSL_ERROR_UNSUPPORTED_VERSION, the owner must enable a currently supported TLS version and compatible configuration. The visitor should not enable obsolete TLS. For a certificate warning, the owner should check validity, hostname coverage, and the certificate chain the server sends. Renewing an expired certificate or installing the required chain can resolve the corresponding error.

If the connection closes during negotiation, the owner should check the HTTPS listener, proxy or load balancer, and server logs for the time of the attempt. A listener receiving HTTPS traffic must be configured to handle TLS on that port. Correct the confirmed configuration problem, then test the exact hostname that failed.

Report the Error and Retest

Give the site owner or network administrator the exact hostname, Firefox warning and code, approximate time and time zone, and the results from other browsers and networks. Keep credentials, session tokens, and private log data out of the report. If you need to contact the organization behind the website while the error remains, use another trusted contact method.

After a repair, open the original HTTPS address in the updated browser on the network where it failed. Confirm that the expected site loads without the warning. If the error remains or its code changes, use that current result to guide the next check instead of bypassing the block.