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 why you might see time-related errors on HTTPS websites and how you can troubleshoot these errors by correcting your system clock.
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.
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.
This page explains the error: "Website will not allow Firefox to display the page if another site has embedded it"
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.
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.
Firefox certificate pinning reports; what they are and why you might want to share yours.
This article presents solutions and workarounds to a failed Firefox update so that you can get it updated and working correctly again.
This article describes the reasons for this error message and covers possible solutions and workarounds.
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.
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 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".
When accessing a site with SSLv3, Firefox will block it and display an "Unable to connect securely" message.
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".
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.
After the update to Firefox 63, some users with Quick Heal security software might be impacted by tabs repeatedly crashing. This article explains how to fix that.
How to disable the Enterprise Roots preference to fix TLS connection errors caused by antivirus software, without compromising security.
Flash 11.3 crashes more frequently than previous versions of Flash. Updating to the latest version of Flash should fix this issue for most people.
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.