Software⏱️ 3 min read📅 2026-06-11

How to Fix: Firefox "invalid certificate" error for a trusted website (sec_error_reused_issuer_and_serial)

Invalid certificate error in Firefox on Mac OS X. Contact server administrator for a new certificate.

Quick Answer: Try clearing Firefox's cache and cookies, then restart the browser.

📋 Table of Contents

  1. ⚠️ Common Causes
  2. ✅ Best Solutions to Fix It
  3. 💡 Conclusion

The 'invalid certificate' error with Firefox, specifically the 'sec_error_reused_issuer_and_serial' error message, can be frustrating for users who are trying to access legitimate websites. This error occurs when the same SSL/TLS certificate is being used by multiple websites or domains, causing confusion for the browser and leading to this specific error.

This issue can be particularly annoying because it may prevent users from accessing their favorite websites, and they know that the website is legitimate. Fortunately, there are steps you can take to resolve this issue.

⚠️ Common Causes

  • The primary reason for this error is that multiple domains or websites are sharing the same SSL/TLS certificate issued by a certificate authority. This can happen when a website's domain name changes and its SSL/TLS certificate is not updated accordingly, causing the browser to show an invalid certificate error.
  • Another possible cause could be a misconfigured certificate chain, where a certificate is being used for multiple domains or websites without proper configuration, leading to this error.

✅ Best Solutions to Fix It

Clearing Firefox's Certificate Cache

  1. Step 1: Open the Firefox browser and go to Preferences by pressing Ctrl + Shift + P (Windows) or Command + Shift + P (Mac).
  2. Step 2: In the Preferences window, click on the 'Advanced' tab.
  3. Step 3: Click on the 'Network' section.
  4. Step 4: Under the 'Certificates' section, select the option that says 'Clear Now' next to the 'SSL/TLS Certificates' field.
  5. Step 5: Click 'OK' to close the Preferences window.
  6. Step 6: Restart Firefox and try accessing the website again.

Updating the SSL/TLS Certificate

  1. Step 1: Contact the website's administrator or email correspondent for further assistance, as they will need to update their SSL/TLS certificate to resolve this issue.
  2. Step 2: If you have access to the server that hosts the website, you can try updating the SSL/TLS certificate manually. This may involve reinstalling the SSL/TLS certificate or obtaining a new one from the certificate authority.
  3. Step 3: After updating the SSL/TLS certificate, restart Firefox and try accessing the website again.

💡 Conclusion

To resolve the 'invalid certificate' error with Firefox, you can try clearing Firefox's certificate cache or updating the SSL/TLS certificate. If you are unable to resolve the issue on your own, it is recommended that you contact the website's administrator or email correspondent for further assistance.

Did this fix your problem?

If not, try searching for specific error codes.

🔍 Search Error Database

❓ Frequently Asked Questions

🛠️ Related Fixes

How to Fix: Pc crashes shortly after launching game (rainbow

Fix Pc crashes shortly after launching game (rainbow six siege). Compl

How to Fix: Installing an APK on a locked down phone

Installing an APK on a locked down phone: Try using a rooted device, e

How to Fix: New PC build- no signal and no clue

Fix New PC build- no signal and no clue. Complete troubleshooting guid