SSL_ERROR_RX_UNKNOWN_RECORD_TYPE

• HTTP server listens on 443 (nginx misconfig)
• Captive portal (hotel Wi-Fi) intercepts and returns HTML
• MITM proxy with broken TLS handling
• Broken load balancer forwards non-TLS
• nginx stream module routes wrong (TCP pass-through broken)

1. openssl s_client -connect host:443 — should show TLS handshake
2. curl -vI https://host — HTTP/2 200 ok?
3. Check nginx config: listen 443 ssl — did you forget ssl?
4. Test from another network — captive portal issue?
5. Enterno SSL for external validation

Check SSL Certificate →

• ERR_SSL_PROTOCOL_ERROR
• NET::ERR_CERT_AUTHORITY_INVALID
• SSL Handshake Failed
• All SSL errors

The SSL_ERROR_RX_UNKNOWN_RECORD_TYPE error in Firefox indicates that the browser received an unknown record type during the SSL/TLS handshake, often due to misconfigured servers, incompatible protocols, or corrupted browser caches. To resolve this, ensure your server is configured to support TLS 1.2 or higher, clear your browser's cache, and verify that your SSL certificate is correctly installed and valid.

The SSL_ERROR_RX_UNKNOWN_RECORD_TYPE error is a common issue encountered by Firefox users when attempting to establish a secure connection to a website. This error signifies that the browser has received an unexpected or unrecognized record type from the server during the SSL/TLS handshake process. The handshake is a critical phase in establishing a secure connection, where both the client (browser) and server agree on the encryption methods and keys to be used.

Several factors can contribute to this error:

• Server Misconfiguration: Incorrect server settings or outdated software can lead to incompatibilities with modern browsers.
• Protocol Mismatch: If the server does not support the required SSL/TLS versions (TLS 1.2 or higher), the browser may not be able to establish a secure connection.
• Corrupted Cache: Cached data or cookies in the browser can interfere with the SSL handshake.
• Invalid SSL Certificate: An improperly configured or expired SSL certificate can also trigger this error.

Understanding the underlying causes of the SSL_ERROR_RX_UNKNOWN_RECORD_TYPE error is essential for troubleshooting and resolving the issue effectively.

To resolve the SSL_ERROR_RX_UNKNOWN_RECORD_TYPE error in Firefox, follow these systematic troubleshooting steps:

1. Check SSL/TLS Configuration: Ensure your server supports TLS 1.2 or higher. You can verify this by running the following command in your terminal:

openssl s_client -connect yourdomain.com:443 -tls1_2

If the connection is successful, your server supports TLS 1.2. If it fails, you may need to update your server configuration.

1. Clear Browser Cache: A corrupted cache can cause handshake issues. To clear the cache in Firefox:

1. Click on the menu button (three horizontal lines) in the top right corner.
2. Select Settings.
3. Go to Privacy & Security.
4. Under Cookies and Site Data, click on Clear Data.
5. Check both options and click Clear.

1. Verify SSL Certificate: Use an SSL checker tool (e.g., SSL Shopper) to ensure that your SSL certificate is correctly installed and valid. Look for any warnings or errors that need addressing.

1. Check Server Logs: Review your server logs for any error messages related to SSL/TLS connections. This can provide insights into why the handshake is failing.

1. Disable QUIC Protocol: In some cases, the QUIC protocol can cause compatibility issues. To disable QUIC in Firefox:

1. Type about:config in the address bar and press Enter.
2. Search for network.http.http3.enabled.
3. Double-click the setting to change it from true to false.

After completing these steps, restart Firefox and try accessing the website again. If the error persists, consider reaching out to your hosting provider for further assistance.