If a website requires a secure connection that cannot be established, Firefox will not connect to protect you and will show you an error page. Learn more.
Learn why you might see time-related errors on HTTPS websites and how you can troubleshoot these errors by correcting your system clock.
This page explains the error: "Website will not allow Firefox to display the page if another site has embedded it"
This article explains what to do if you see the error message “The bookmarks and history system will not be functional” when you start Firefox.
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.
Firefox shows you a warning page about a potential security risk when you try to connect to a secure site but your connection is not secure.
How to disable the Enterprise Roots preference to fix TLS connection errors caused by antivirus software, without compromising security.
Why Firefox may show you a Secure Connection Failed error when you try to access the configuration page for your router and what to do.
This article describes the reasons for this error message and covers possible solutions and workarounds.
When accessing a site with SSLv3, Firefox will block it and display an "Unable to connect securely" message.
How to start Firefox if you see an error message, "Firefox is already running, but is not responding" or, on macOS, "A copy of Firefox is already open".
This article presents solutions and workarounds to a failed Firefox update so that you can get it updated and working correctly again.
On Linux, the profile path is required to be valid UTF-8. Names of downloaded files are encoded in UTF-8 regardless of glibc and glib settings.
Some websites that need a specific browser or version make a mistake detecting your installed version of Firefox. We'll explain how to fix or work around this.
If you see "Firefox Updated" or "You've been updated to the latest version of Firefox" every time you start Firefox, we'll show you how to fix it.
When connecting to a website that uses an invalid TLS certificate or weak encryption, Firefox will display an error page saying "Your connection is not secure".
How to fix the error ''Your Firefox profile cannot be loaded. It may be missing or inaccessible'' so that you can start and run Firefox.