SSL_ERROR_NO_CYPHER_OVERLAP — Firefox & No Shared Ciphers

Enterno.io Editorial Team

SSL_ERROR_NO_CYPHER_OVERLAP in Firefox

By Anatoly Oshmanovsky · Updated Apr 17, 2026

Key idea:

SSL_ERROR_NO_CYPHER_OVERLAP — Firefox (same as ERR_SSL_VERSION_OR_CIPHER_MISMATCH in Chrome) could not agree on a TLS cipher suite with the server. Both sides have allowed-cipher lists but they don't intersect. Causes: server on legacy ciphers (RC4, 3DES), Firefox dropped weak ones. Fix: enable AES-GCM + ChaCha20-Poly1305 on the server.

This error blocks HTTPS access. Below: causes, fixes, working config, FAQ.

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Common Causes

Server supports only 3DES / RC4 (Firefox removed them in 2020)
Server AES-CBC only; Firefox prefers AES-GCM
Server has ECDHE cipher suites (PFS) disabled
Custom OpenSSL config disallowed modern ciphers
TLS 1.3 not enabled; TLS 1.2 cipher list too narrow

Step-by-Step Fix

nginx modern config: ssl_ciphers TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
Apache: SSLCipherSuite HIGH:!aNULL:!MD5:!3DES:!RC4
Enable TLS 1.3 (ssl_protocols TLSv1.2 TLSv1.3)
Mozilla SSL Config Generator: ssl-config.mozilla.org
Verify via Enterno SSL — shows supported ciphers

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Related SSL Errors

CertificateExpiry, issuer, domains (SAN)

ChainIntermediate and root CA validation

TLS ProtocolTLS version and cipher suite

VulnerabilitiesHeartbleed, POODLE, weak ciphers

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Common Mistakes

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Expired certificateBrowsers block sites with expired SSL. Set up auto-renewal or monitoring.

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Incomplete certificate chainWithout intermediate CA, some browsers and bots cannot verify the certificate.

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Mixed content on HTTPS siteHTTP resources on an HTTPS page — the browser lock icon disappears, reducing trust.

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Using TLS 1.0/1.1Legacy TLS versions have known vulnerabilities. Use TLS 1.2+ or 1.3.

❌

Domain mismatch in certificateThe certificate must cover all site domains, including www and subdomains.

Best Practices

✓

Set up auto-renewalLet's Encrypt + certbot with cron — certificate renews automatically every 60-90 days.

✓

Enable HSTSStrict-Transport-Security header forces browsers to always use HTTPS.

✓

Use TLS 1.3TLS 1.3 is faster (1-RTT handshake) and safer — legacy ciphers removed.

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Monitor expiration datesCreate a monitor on Enterno.io — get notified well before expiration.

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Verify chain after renewalAfter certificate renewal, confirm that intermediate certificates are installed.

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How-to

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Research

TLS Cipher Suites 2026: Distribution Report

Errors

Alternatives

Frequently Asked Questions

Why is Firefox stricter than Chrome?

Mozilla's NSS takes a more conservative stance. AES-CBC without SHA-256 — Firefox rejects since 2022, Chrome still accepts.

Will legacy Windows clients work?

Windows XP + Firefox — no, SHA-1 signatures blocked. Windows 7 + Firefox 78+ — OK for AES-GCM.

How do I test cipher matching?

<code>openssl s_client -connect example.com:443 -cipher ECDHE-RSA-AES128-GCM-SHA256</code>. Error = not supported.

Switching from 3DES to AES, will I lose users?

Only IE 6/7 on XP. In 2026 statistically zero.