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.
Malware is software designed to invade a computer without your knowledge. We'll explain common symptoms, how to prevent it being installed and how to remove it.
Most issues with Firefox can be solved by working through these troubleshooting steps. Just start at the beginning and keep going until the problem is fixed.
Use Firefox "Troubleshoot Mode" (known as "Safe Mode" in previous versions of Firefox) to diagnose and fix problems. Learn more.
Learn how to find out if an extension, theme or hardware acceleration is causing a Firefox problem and what steps you can take to fix it.
When troubleshooting Firefox problems, resetting user preferences can be helpful in pinpointing the issue. This article explains how to do it.