firefox
Firefox Network Error Codes
Network and security error codes displayed by Firefox (and other Gecko-based browsers) when a page fails to load. They appear on the built-in error page and are defined as NS_ERROR_*, SEC_ERROR_*, SSL_ERROR_* and MOZILLA_PKIX_ERROR_* constants in the Firefox/NSS source.
18 codes
references searchfox.org/mozilla-central/source/xpcom/base/ErrorList.pysupport.mozilla.org/en-US/kb/what-do-network-error-messages-mean
· All codes 18 codes
- MOZILLA_PKIX_ERROR_MITM_DETECTED Possible Man-in-the-Middle Detected Firefox's certificate verifier detected a pattern characteristic of TLS-intercepting security or antivirus software rather than a malicious attacker, and blocked the connection as a precaution.
- NS_BINDING_ABORTED Load Aborted The network request was cancelled before it completed, typically because the user navigated away, stopped the load, or the tab was closed.
- NS_ERROR_CONNECTION_REFUSED Unable to Connect The remote host actively refused the TCP connection, typically because no service is listening on the requested port or a firewall rejected it outright.
- NS_ERROR_CORRUPTED_CONTENT Content Encoding Error The content received from the server was corrupted, most often a response declared with an encoding (such as gzip or brotli) that doesn't actually match the bytes sent.
- NS_ERROR_DOCUMENT_NOT_CACHED Document Expired From Cache The page was requested from the browser cache (for example via back/forward navigation) but is no longer available there and cannot be reloaded from the network in this context.
- NS_ERROR_MALFORMED_URI Malformed URI The requested address is not a valid URI, for example due to invalid characters or a broken scheme, and could not be parsed well enough to attempt a load.
- NS_ERROR_NET_INTERRUPT Connection Interrupted The connection was interrupted while the page was transferring data, so the load could not complete. Commonly seen when navigation is cancelled mid-transfer or the network drops.
- NS_ERROR_NET_RESET Connection Reset The connection to the server was reset while the page was loading, usually because the server or an intermediate proxy closed the TCP connection unexpectedly.
- NS_ERROR_NET_TIMEOUT Connection Timed Out The connection to the server timed out before a response was received. Often caused by network congestion, a firewall silently dropping packets, or an overloaded server.
- NS_ERROR_OFFLINE Browser Is Offline The request could not be made because Firefox is currently in offline mode (Work Offline), so no network connections are attempted.
- NS_ERROR_PROXY_CONNECTION_REFUSED Proxy Server Refused Connection The configured proxy server refused the connection. Check the browser's network/proxy settings, or that the proxy service is actually running and reachable.
- NS_ERROR_REDIRECT_LOOP Redirect Loop Detected The server issued a series of redirects that loop back on themselves, so the page can never finish loading. Shown as "The page isn't redirecting properly."
- NS_ERROR_UNKNOWN_HOST Server Not Found DNS resolution failed for the requested hostname. Shown as "Hmm. We're having trouble finding that site." Usually means the domain doesn't exist, was mistyped, or the DNS resolver is unreachable.
- NS_ERROR_UNKNOWN_PROTOCOL Protocol Not Recognized Firefox does not know how to handle the URI's scheme (for example an unregistered custom protocol) and has no handler registered to open it.
- NS_ERROR_UNKNOWN_PROXY_HOST Proxy Server Not Found DNS resolution failed for the configured proxy server's hostname. Indicates a misconfigured proxy address in the browser's network settings.
- SEC_ERROR_EXPIRED_CERTIFICATE Certificate Expired The server's TLS certificate has passed its validity period. Firefox blocks the connection until the site renews the certificate or the client's clock is corrected.
- SEC_ERROR_UNKNOWN_ISSUER Unknown Certificate Issuer The certificate authority that issued the server's TLS certificate is not trusted by Firefox's certificate store, often seen with self-signed certificates or an incomplete chain.
- SSL_ERROR_BAD_CERT_DOMAIN Certificate Domain Mismatch The server's TLS certificate is valid but was not issued for the requested hostname, so Firefox refuses the connection. Shown on the "Did Not Connect: Potential Security Issue" page.