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.
SSL Issues?
Open a Support TicketQuick Recap
- Check SSL/TLS Status in cPanel and run AutoSSL if needed
- Clear browser cache after certificate changes
- Check Cloudflare SSL mode if using Cloudflare
- Update Firefox to the latest version
- Disable antivirus SSL scanning to test
SSL troubleshooting · Last updated March 2026 · Browse all SSL articles
