Mozilla Firefox Error Code MOZILLA_PKIX_ERROR_MITM_DETECTED: How to Fix It
Medium 20-45 minutes Critical Severity
Verified June 2026
- Error Code
- MOZILLA_PKIX_ERROR_MITM_DETECTED
- Brand
- Mozilla Firefox
- Product Type
- browser
- Severity
- Critical
- DIY Difficulty
- Medium
- Estimated Fix Time
- 20-45 minutes
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Tools You'll Need
- Internet connection
- Administrative access to computer
How to Fix Error Code MOZILLA_PKIX_ERROR_MITM_DETECTED
-
Check Your Network Connection
Never ignore this error on public Wi-Fi as it could indicate an actual security threat -
Temporarily Disable Antivirus SSL Scanning
Remember to re-enable this protection after testing -
Clear Firefox SSL State
-
Reset Firefox Network Settings
Only modify these settings if you understand the security implications -
Check Corporate or School Network Settings
-
Update Firefox and System
-
Create New Firefox Profile
You'll need to reconfigure your bookmarks and extensions in the new profile
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When to Call a Professional
Contact your IT administrator if this occurs on a corporate network, or seek professional cybersecurity help if you suspect an actual man-in-the-middle attack. If the error persists across all networks and devices, consult a computer technician.Frequently Asked Questions
What does MOZILLA_PKIX_ERROR_MITM_DETECTED actually mean?
This error means Firefox detected that something is intercepting your secure connection, potentially a man-in-the-middle attack. However, it often triggers false positives from legitimate security software or corporate firewalls.
Is it safe to bypass this Firefox security warning?
Generally no, especially on public networks. Only bypass if you're certain the source is legitimate, such as known corporate security software or after consulting with your IT administrator.
Why does this error only appear in Firefox and not other browsers?
Firefox has more stringent certificate validation than some browsers. This enhanced security can catch threats others miss but may also create more false positives with legitimate security tools.
Can antivirus software cause this Firefox MITM error?
Yes, antivirus programs with SSL/HTTPS scanning features commonly trigger this error because they intercept secure connections to scan for threats, which Firefox interprets as a potential attack.
Will resetting Firefox fix the MITM detection error permanently?
Resetting Firefox may resolve configuration issues causing false positives, but if the underlying cause (like antivirus software or network configuration) isn't addressed, the error may return.