How to Fix MOZILLA_PKIX_ERROR_MITM_DETECTED error on Firefox in Windows 10

If you’re having some problem browsing multiple websites on the Firefox browser on your Windows 10 computer, then this post might be of help. One of the most common problems you could encounter in Firefox is mostly related to HTTPS and one of them is the MOZILLA PKIX ERROR MITM DETECTED or ERROR SELF SIGNED CERT or SEC ERROR UNKNOWN ISSUER error which means that Firefox was unable to trust certificates issued on secured websites.

If you encounter the MOZILLA_PKIX_ERROR_MITM_DETECTED error in Firefox, this indicates that something in your network or system is interrupting your connection and injecting certificates and when that happens, Firefox won’t trust it. In such cases, one of the culprits is malware. Malware will try to replace a legitimate certificate with its certificate. Another cause is security software where it keeps a tab on a secure connection and creates a false positive, for instance:

“In Microsoft Windows accounts protected by Family Safety settings, secure connections on popular websites like Google, Facebook and YouTube might be intercepted and their certificates replaced by a certificate issued by Microsoft in order to filter and record search activity.”

And if you are connected to a corporate network, there might be a monitoring/filtering product that could be replacing certificates. Moreover, there are also users who reported getting this issue when they use the Nightly version of Firefox. And if that’s the case, you have to try accessing secure websites using only the stable build especially when it comes to payments. However, if you are not doing that, then here are some options you need to check out.

Option 1 – Try turning off HTTPS Scanning on your security and antivirus programs

Each security-based software has a security option that allows you to turn off the HTTPS scanning functionality. They may be available under different names such as HTTPS Scanning, Scan SSL, Show safe result, Do not scan encrypted connections, etc. Find what is applicable for your security or antivirus software and then try turning it off temporarily and see if it helps in fixing the MOZILLA_PKIX_ERROR_MITM_DETECTED error in Firefox.

Option 2 – Try to disable security.enterprise_roots.enabled

The next thing you can do if the first option didn’t work is to disable security.enterprise_roots.enabled which is an HTTPS certificate check on Firefox. Note that this is not recommended but you have to at least try in order to fix the error.

  • Open Firefox and then type “about: config” in the Firefox address bar and hit Enter.
  • After that, if an info message appears, confirm it.
  • Next, search for the security.enterprise_roots.enabled preference and once you found it, double click on it.
  • Then change its value to true and restart the Firefox browser once. This will import all the custom certificates from the other security software into Firefox. As a result, it will make sure to mark those sources as trusted and you won’t get the MOZILLA_PKIX_ERROR_MITM_DETECTED error.

Congratulations, you have just fixed the MOZILLA_PKIX_ERROR_MITM_DETECTED error in Windows 10 all by yourself. If you would like to read more helpful articles and tips about various software and hardware visit errortools.com daily.

Now that’s how you fix the MOZILLA_PKIX_ERROR_MITM_DETECTED error in Windows 10 on a computer. On the other hand, if your computer is going through some system-related issues that have to get fixed, there is a one-click solution known as Restoro you could check out to resolve them. This program is a useful tool that could repair corrupted registries and optimize your PC’s overall performance. Aside from that, it also cleans out your computer for any junk or corrupted files that help you eliminate any unwanted files from your system. This is basically a solution that’s within your grasp with just a click. It’s easy to use as it is user-friendly. For a complete set of instructions in downloading and using it, refer to the steps below

Perform a full system scan using Restoro. To do so, follow the instructions below.

  1. Download and install Restoro from the official site.
  2. Once the installation process is completed, run Restoro to perform a full system scan.
    restoro application screen
  3. After the scan is completed click the “Start Repair” button.
    restoro application screen
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