Firefox Edge Browser Error Code MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE: How to Fix It

Medium 10-30 minutes Medium Severity Verified June 2026
Summarize with ChatGPTSummarize with ClaudeSummarize with Perplexity Add as Preferred Source on Google
Error Code
MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE
Brand
Firefox Edge
Product Type
browser
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
10-30 minutes
The MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE error in Firefox means the browser detected that the SSL/TLS certificate presented by a website does not match the expected public key pin stored for that site — a security feature called HTTP Public Key Pinning (HPKP). This usually happens when antivirus software, a corporate network proxy, or a VPN intercepts your HTTPS connection and substitutes its own certificate, triggering Firefox's built-in security check. In most cases you can resolve this yourself by adjusting security software settings or Firefox configuration, but you should never simply ignore this error on sensitive sites like banks or email providers.
Ad

Tools You'll Need

How to Fix Error Code MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE

  1. Note the Exact Site and Error Details

    Never click through or bypass this error on banking, email, government, or any site where you enter a password or payment details unless you are 100% certain the interception is from your own trusted security software.

  2. Disable HTTPS Scanning in Your Antivirus Software

    Disabling HTTPS scanning reduces your antivirus protection slightly. Only do this if you trust the sites you visit. Re-enable it if you do not need the fix urgently.

  3. Disable or Reconfigure Your VPN or Proxy

  4. Check for Corporate Network or Firewall Interception

    Do not attempt to bypass corporate security controls without authorization from your IT department. Doing so may violate your organization's acceptable use policy.

  5. Clear Firefox's HPKP Cache (Pinning Database)

    Only delete the SiteSecurityServiceState file, not other profile files. Deleting other files can cause you to lose saved passwords, bookmarks, or settings.

  6. Update Firefox to the Latest Version

  7. Test in Firefox Safe Mode and a Fresh Profile

  8. Check Your System Date and Time

  9. Report the Issue to the Website Owner (If None of the Above Apply)

Ad

When to Call a Professional

Contact your IT department or a professional technician if you are on a managed corporate or school network where you do not have admin rights to change security settings — only your network administrator can add SSL inspection exceptions. If you suspect the error is caused by malware or a man-in-the-middle attack (the certificate issuer is completely unknown and you are on a home network with no security software installed), run a full malware scan immediately using reputable security software or consult a cybersecurity professional. If the error affects a website you manage, contact your web hosting provider or SSL certificate authority to investigate a possible certificate misconfiguration.

Frequently Asked Questions

Is MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE dangerous to ignore?
On sensitive sites like banks, email providers, or any site where you log in or enter payment information, you should never ignore this error. It could indicate a man-in-the-middle attack intercepting your connection. On sites you manage yourself or on an internal corporate network where IT has confirmed SSL inspection is in place, it is generally safe to investigate and resolve using the steps above. Never simply click through without understanding the cause.
Why does this error only happen in Firefox and not in Chrome or Edge?
Firefox is the only major consumer browser that still enforces HTTP Public Key Pinning (HPKP) for third-party sites. Google Chrome and Microsoft Edge dropped strict HPKP enforcement for non-built-in pins in 2018. This is why you may see this error in Firefox but not in other browsers — it does not mean Chrome or Edge are safer; it means they no longer check for pin mismatches in the same way.
Will deleting SiteSecurityServiceState.txt cause me to lose my bookmarks or passwords?
No. The SiteSecurityServiceState file only stores HSTS (HTTP Strict Transport Security) and HPKP pin data that Firefox has learned from websites. Deleting it will not affect your bookmarks, saved passwords, history, extensions, or any other browser data. Firefox will simply rebuild the file as you visit sites again.
Can antivirus software really cause this Firefox error?
Yes, this is one of the most common causes. Antivirus programs that include HTTPS or SSL scanning features work by inserting themselves as a 'trusted' intermediary between your browser and websites. They decrypt your traffic to scan it, then re-encrypt it using their own certificate. Firefox's HPKP system detects that the certificate is not the one the website pinned, and blocks the connection. Disabling HTTPS scanning in your antivirus, or adding Firefox as an exception, almost always resolves this.
How do I find my Firefox profile folder on Windows, Mac, and Linux?
On Windows, press Win+R, type '%APPDATA%\Mozilla\Firefox\Profiles\' and press Enter. On macOS, open Finder, press Cmd+Shift+G, and type '~/Library/Application Support/Firefox/Profiles/'. On Linux, open your file manager or terminal and navigate to '~/.mozilla/firefox/'. In each case you will see one or more folders ending in '.default' or '.default-release' — that is your active profile folder where the SiteSecurityServiceState file is located.

Related Error Codes