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By Eunice Samson | May 10, 2019 |

greater than 2 minutes

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Mozilla Firefox continues to be one of the most popular web browsers across the globe. Even during its beta phase, it was lauded for its security, speed, and efficient add-ons. However, like other browsers, it is also prone to issues. For example, many Firefox users are having trouble accessing various websites, especially those with an HTTPS prefix. Most of them get the following error messages:


It is worth noting that these error messages indicate that your web browser does not trust the integrity of the certificates issued to the websites you’re visiting. The great news is, there are still ways to access the sites. In this post, we will teach you how to fix the ‘MOZILLA_PKIX_ERROR_MITM_DETECTED’ issue.


If you saw this error message, it is likely that something on your network or system is disrupting your connection and certificates. Consequently, Firefox ends up distrusting the certificates. Usually, this happens when malware attempts to use its certificate to replace a legitimate certificate. As such, it is crucial that you have reliable security software on your computer to prevent this problem.

There are many antivirus software programs out there, but Auslogics Anti-Malware is the product that can provide you with comprehensive protection. Aside from checking your system memory for malicious programs, it also scans your browser extensions. It prevents data leaks and detects suspicious items that may threaten the security of your computer.


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Most of the users affected by the problem mentioned that the issue occurred on the Nightly version of Firefox. If this is the case, then you can try using a stable build to access secure websites. However, if that does not work, you can always learn how to troubleshoot security error codes on secure websites, using Firefox. Here are the methods:

If you cannot resolve the
problem yourself, you can
ask our certified PC technicians for immediate assistance in the chat right on this page.

Method 1: Switching Off the HTTPS Scanning Feature

You can configure the security options of any anti-virus software program. So, if your security software has HTTPS scanning functionality, we suggest that you switch it off. It is worth noting that you may find this feature under various names, including the following:

  • Scan SSL
  • Do not scan encrypted connections
  • Show safe results

Method 2: Disabling the HTTPS Scanning Feature on Firefox

It is not recommended to disable the HTTPS scanning functionality on Firefox. However, this can be your last resort for fixing the ‘MOZILLA_PKIX_ERROR_MITM_DETECTED’ error.

  1. Launch Mozilla Firefox.
  2. Inside the URL box, type “about:config” (no quotes), then hit Enter.
  3. If an info message shows up, click the ‘I accept the risk!’ button.
  4. Look for the security.enterprise_roots.enabled entry.
  5. Once you find it, double-click it.
  6. Modify the value to ‘true’.
  7. Restart Firefox.

After performing the steps above, Firefox will import all the custom certificates from other security software programs on your computer. Consequently, the process will ensure that the sources can be trusted from now on, and you will cease to see the ‘MOZILLA_PKIX_ERROR_MITM_DETECTED’ error message.

Can you recommend other methods for resolving the ‘MOZILLA_PKIX_ERROR_MITM_DETECTED’ error?

Join the discussion below and share your tips with our readers!

Fed up with your slow PC? Tired of waiting for Windows to start up? Take a look at the most common reasons behind poor performance and the best ways to deal with them here.


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