Mozilla Firefox is a household name when it comes to web browsers. It is reliable and proven to be effective and easy to use. But, there are times when some users encounter an error when browsing the web on Firefox. One example of this browsing issues is the MOZILLA_PKIX_ERROR_MITM_DETECTED error.

The MOZILLA_PKIX_ERROR_MITM_DETECTED Firefox browser error code occurs when there is a security issue with your network connection. It is mostly a trust issue with Firefox since there are privacy certificates that your browser cannot trust. Fortunately, some solutions prove to help fix the problem.



If you encounter the MOZILLA_PKIX_ERROR_MITM_DETECTED security error code, you are not alone. Many users also reported the same problem when they browse on Firefox. To help you solve the issue, continue reading below and find the methods on how you can fix it. Follow each step and try to check if the problem is still there.

Method #1 – Disable VPN or Proxy Server

Turn Off Proxy Server

  • Launch the Windows Run Dialog Box. You can press both Windows key + R.
  • Type ms-settings:network-proxy and hit Enter.
  • Go to Proxy.
  • Look for the Manual proxy setup on the right side of the window.
  • Toggle the button to Disable.
  • Restart your computer.

Turn Off VPN

  • On your Control Panel menu, navigate to Programs and Features.
  • Look for the VPN server you are using.
  • Right-click on the name and select Uninstall.
  • Follow the instructions to uninstall your VPN.
  • Restart your computer.

Method #2 – Disable security.enterprise_roots.enabled on Firefox Settings

Screenshot: Windows Dispatch
  • Launch your Firefox browser.
  • On the address bar, type about:config. Hit Enter.
  • A confirmation message will appear. Click OK or Yes.
  • Look for security.enterprise_roots.enabled.
  • Double-click on it to change the value to True.
  • Restart your Firefox browser.

Method #3 – Temporarily Disable or Uninstall Your Antivirus Software

Credit: Krisikorn/Freepik

Please note that uninstalling your antivirus software leaves your system vulnerable to various malware and other malicious attacks. We suggest that you disable it temporarily and check if the issue persists. If it is still there, then you will have to look for a new antivirus program you can use before uninstalling the current one.

  • Open the Control Panel.
  • Go to Programs and Features.
  • Look for your Antivirus software and right-click on it.
  • Select Uninstall.
  • Restart your computer.

Which of the methods above helped you resolve your Firefox browser network privacy error? We would love to know what works, so tell us in the comments below.


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