SSL_ERROR_RX_RECORD_TOO_LONG is a Firefox-specific error that occurs when the browser receives an SSL/TLS record that exceeds the maximum allowed size of 16,384 bytes (16 KB). In practice, this almost always means the web server is sending plain HTTP data in response to an HTTPS request. The unencrypted HTTP response is interpreted as an oversized SSL record, triggering the error.
This error is the Firefox equivalent of Chrome’s ERR_SSL_PROTOCOL_ERROR and typically indicates a server misconfiguration rather than a client-side problem. However, several client-side factors can contribute, and there are fixes for both visitors and site owners.
What Causes SSL_ERROR_RX_RECORD_TOO_LONG
The most common cause is a web server that is not configured for SSL/TLS on port 443. When you request https://example.com, your browser connects to port 443 and expects an SSL handshake. If the server on port 443 serves plain HTTP instead of initiating SSL, the HTTP response data is too large to be a valid SSL record, and Firefox displays this error.
Specific server-side causes include: missing or incorrect SSL virtual host configuration in Apache (the default non-SSL vhost responds on port 443), expired or missing SSL certificate files referenced in the server config, Nginx or Apache not loading the SSL module, a reverse proxy forwarding HTTPS traffic to an HTTP backend incorrectly, and SSL certificate path errors where the server cannot find the cert and falls back to HTTP.
Fix 1: Try HTTP Instead of HTTPS
If the server does not support HTTPS, manually change the URL from https:// to http:// in the address bar. If the page loads over HTTP, the server is not configured for SSL on that domain. This is a server-side issue that the website administrator needs to fix. For your own safety, avoid submitting any sensitive data (passwords, payment information) over an unencrypted HTTP connection.
Fix 2: Clear Browser SSL Cache
Firefox caches SSL session data that can become corrupted. Go to Firefox Settings (about:preferences), Privacy & Security, scroll to Certificates, and click “View Certificates.” In the Certificate Manager, go to the “Servers” tab and remove any entries for the affected domain. Also clear your Firefox cache: press Ctrl+Shift+Delete, select “Everything,” check “Cache” and “Cookies,” then click “Clear Now.”
Fix 3: Check Your System Clock
An incorrect system date and time can cause SSL errors including this one. SSL certificates have validity periods and your system clock must be within that range. On Windows, right-click the clock, select “Adjust date/time,” and enable “Set time automatically.” On macOS, go to System Settings, General, Date & Time, and enable automatic time setting. Restart Firefox after correcting the time.
Fix 4: Fix Server SSL Configuration (Site Owners)
Check that your web server has a proper SSL virtual host for the domain. In Apache, verify that the VirtualHost on port 443 includes SSLEngine On, SSLCertificateFile, and SSLCertificateKeyFile directives with correct file paths. Test your configuration with “apachectl configtest” or “nginx -t” before restarting. Common fixes: ensure mod_ssl is enabled (“a2enmod ssl” on Ubuntu), verify certificate files exist and are readable, and make sure the 443 VirtualHost is separate from the port 80 VirtualHost.
Fix 5: Check for Proxy or CDN Issues
If your site uses Cloudflare or another CDN/proxy, the SSL configuration between the CDN and your origin server may be incorrect. In Cloudflare, go to SSL/TLS settings and make sure the encryption mode matches your origin server’s SSL setup. “Full (Strict)” requires a valid SSL certificate on your origin. “Flexible” sends HTTP to your origin, which works if your origin does not have SSL but can cause redirect loops. “Full” requires any SSL certificate on the origin, including self-signed.
Frequently Asked Questions
Why does this error only appear in Firefox?
SSL_ERROR_RX_RECORD_TOO_LONG is a Firefox-specific error message. Chrome and Edge display the same underlying problem as ERR_SSL_PROTOCOL_ERROR or a generic connection error. The root cause is identical across browsers: the server is sending non-SSL data on an SSL port. If you see this error in Firefox, the same site will likely fail in other browsers too, just with a different error message.
Can a VPN cause SSL_ERROR_RX_RECORD_TOO_LONG?
Rarely. A VPN that intercepts and re-encrypts HTTPS traffic could potentially cause this error if its SSL proxy is misconfigured. More commonly, VPNs that inject ads or modify traffic can corrupt SSL sessions. Disconnect your VPN and test the site directly. If it works without the VPN, the VPN’s traffic handling is the problem.
Does this error mean the website is insecure?
It means the website’s SSL/TLS is not functioning correctly, which could expose data to interception. Do not submit sensitive information on a site showing this error. If you are the site owner, fixing the SSL configuration is critical because browsers will block access for all visitors, and search engines may deindex HTTPS URLs that do not serve valid SSL responses.
