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Firefox SEC_ERROR_UNKNOWN_ISSUER

Errorfirefox

Overview

Firefox SEC_ERROR_UNKNOWN_ISSUER means the SSL certificate was issued by an authority that Firefox does not recognize or trust.

Key Details

  • Firefox shows "Warning: Potential Security Risk Ahead"
  • Certificate issuer not in Firefox trusted root store
  • Firefox uses its own certificate store (not OS)
  • Different from Chrome which uses the OS certificate store

Common Causes

  • Self-signed certificate on the server
  • Corporate proxy SSL inspection with custom CA
  • Antivirus performing HTTPS scanning
  • Incomplete certificate chain on the server

Steps

  1. 1Check if antivirus is scanning HTTPS — disable HTTPS scanning
  2. 2For corporate networks: import company CA into Firefox
  3. 3Click Advanced > Accept the Risk (only for trusted sites)
  4. 4Contact site owner about incomplete certificate chain

Tags

browserfirefoxfirefox sec error unknown issuerfixtroubleshooting

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Frequently Asked Questions

Firefox uses its own certificate store — Chrome uses the OS store which may have the corporate CA.