Firefox : Secure Connection Failed An error occurred during a

Knowledgebase

SSL & HTTPS | Updated 2026

The "Secure Connection Failed" error in Firefox means the browser cannot establish an encrypted connection to the server. The error message usually includes technical details like "SSL received a record that exceeded the maximum permissible length."

Most Likely Cause

SSL certificate is missing or misconfigured

Check your SSL status in cPanel > Security > SSL/TLS Status. If your domain does not have a certificate, click "Run AutoSSL" to generate a free one. If it shows as valid but Firefox still errors, clear your browser cache and try again.

01. Other Causes

Mixed HTTP/HTTPS configuration - Your site may be trying to serve HTTPS content over port 80, or vice versa. Make sure your site URL uses https:// consistently.
Firewall or antivirus interference - Some security software intercepts HTTPS connections. Try temporarily disabling your antivirus SSL scanning to test.
Outdated browser - Very old Firefox versions may not support the TLS version the server requires. Update Firefox to the latest version.
Cloudflare SSL mode - If you use Cloudflare, make sure the SSL mode is set to "Full (Strict)," not "Flexible." See Cloudflare Guide.

For the Chrome equivalent of this error, see ERR_SSL_VERSION_OR_CIPHER_MISMATCH. For general SSL setup, see SSL Certificates and HTTPS.