Error messages: what they mean and how to fix
How to troubleshoot error messages on Firefox
Secure connection failed and Firefox did not connect
If a website requires a secure connection that cannot be established, Firefox will not connect and will show you an error page. Learn more.
How to troubleshoot time related errors on secure websites
Learn why you might see time-related errors on HTTPS websites and how you can troubleshoot these errors by correcting your system clock.
Fix "The bookmarks and history system will not be functional" error message
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.
What do the security warning codes mean?
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.
Website will not allow Firefox to display the page if another site has embedded it
This page explains the error: "Website will not allow Firefox to display the page if another site has embedded it"
How to disable the Enterprise Roots preference
How to disable the Enterprise Roots preference to fix TLS connection errors caused by antivirus software, without compromising security.
How to troubleshoot security error codes on secure websites
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.
Certificate contains the same serial number as another certificate
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.
How to fix the Update Failed error message when updating Firefox
This article presents solutions and workarounds to a failed Firefox update so that you can get it updated and working correctly again.
Warning Unresponsive script - What it means and how to fix it
This article describes the reasons for this error message and covers possible solutions and workarounds.
"Firefox is already running but is not responding" error - How to fix
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".
Firefox says it's just updated every time it starts - how to fix
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.
What do the SSLv3 error messages mean on Firefox?
When accessing a site with SSLv3, Firefox will block it and display an "Unable to connect securely" message.
File system paths on Linux are always treated as UTF-8
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.
Websites say that Firefox is outdated or incompatible even though it's the latest version
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.
How to resolve weak crypto error messages on Firefox
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 run Firefox when your profile is missing or inaccessible
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.