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If a website requires a secure connection that cannot be established, Firefox will not connect and will show you an error page. Learn more.
Learn about the error codes SEC_ERROR_UNKNOWN_ISSUER MOZILLA_PKIX_ERROR_MITM_DETECTED and ERROR_SELF_SIGNED_CERT on HTTPS websites and how to troubleshoot.
Enhanced Tracking Protection in Firefox automatically protects your privacy while you browse.
Firefox automatically updates itself by default, but you can always do a manual update. Learn how to update Firefox on Windows, Mac, or Linux.