Firefox Edge Browser Error Code SEC_ERROR_BAD_SIGNATURE: How to Fix It

Medium 15-45 minutes Medium Severity Verified June 2026
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Error Code
SEC_ERROR_BAD_SIGNATURE
Brand
Firefox Edge
Product Type
browser
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
15-45 minutes
The SEC_ERROR_BAD_SIGNATURE error in Firefox means the browser has detected that a website's SSL/TLS certificate has an invalid or untrustworthy cryptographic signature. This typically happens when a certificate has been tampered with, is improperly issued, or when something on your system — such as security software or a misconfigured network — is intercepting your encrypted connection. While this is a medium-severity error, it is important to address it carefully because bypassing it without understanding the cause could expose your data to security risks.
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Tools You'll Need

How to Fix Error Code SEC_ERROR_BAD_SIGNATURE

  1. Reload the Page and Check the URL

    Do not proceed to a website that consistently throws this error without understanding why — it could indicate a man-in-the-middle attack or a compromised certificate.

  2. Check Your System Date and Time

  3. Disable Antivirus SSL/HTTPS Scanning

    Only disable SSL scanning temporarily for testing. Re-enable it after diagnosing the issue to maintain your system's security.

  4. Clear Firefox's Certificate Cache and Browsing Data

  5. Reset Firefox's Certificate Store (cert9.db)

    Renaming cert9.db will remove any manually trusted or distrusted certificates you have previously configured. Note those settings before proceeding if needed.

  6. Check for Corporate or Network Proxy Interference

  7. Update Firefox to the Latest Version

  8. Test in a New Firefox Profile or Another Browser

  9. Disable Firefox Extensions Temporarily

  10. Refresh Firefox (Reset to Default Settings)

    Refreshing Firefox will remove all extensions, customizations, and site-specific permissions. Your bookmarks, history, and saved passwords will be kept.
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When to Call a Professional

If the SEC_ERROR_BAD_SIGNATURE error appears on multiple websites across multiple browsers and devices on your network simultaneously, your router or ISP may be the source of the interference — contact your ISP or a network technician. If you are on a corporate or institutional network and cannot resolve the error after disabling antivirus SSL scanning, escalate the issue to your IT department, as they may need to deploy a trusted root certificate to your device. If you suspect your device has been compromised by malware that is intercepting your HTTPS traffic, run a full malware scan using a reputable tool (such as Malwarebytes) or consult a cybersecurity professional.

Frequently Asked Questions

Is SEC_ERROR_BAD_SIGNATURE dangerous to ignore?
It depends on the context. If the error appears only on one obscure site, it may simply have a misconfigured certificate. However, if it appears on trusted sites like your bank or email provider, do not ignore it — it could indicate a man-in-the-middle attack where someone is intercepting your connection. Always investigate the cause before bypassing the warning.
Why does SEC_ERROR_BAD_SIGNATURE only appear in Firefox and not Chrome or Edge?
Firefox uses its own built-in certificate store and validation engine, separate from the operating system's. Chrome and Edge typically use the Windows or macOS system certificate store. If your antivirus or employer has added a trusted certificate to the system store but not to Firefox's store, Firefox will flag it as invalid while other browsers accept it. The fix is to import the required root certificate into Firefox's certificate manager under Settings > Privacy & Security > View Certificates.
How do I add an exception for SEC_ERROR_BAD_SIGNATURE in Firefox?
On the Firefox error page, scroll down and look for an 'Advanced' button. Click it, then click 'Accept the Risk and Continue' to add a one-time exception. To add a permanent exception, go to Settings > Privacy & Security > View Certificates > Servers tab and add the site manually. However, only do this for sites you fully trust, such as a local development server or an internal corporate tool — never for public websites.
Can a VPN cause SEC_ERROR_BAD_SIGNATURE in Firefox?
Yes, some VPN clients — especially those with built-in ad blocking or HTTPS inspection features — can interfere with certificate validation in Firefox. Try disconnecting from your VPN and reloading the page. If the error disappears, check your VPN's settings for any SSL inspection or HTTPS filtering options and disable them, or add the affected site as an exception within the VPN software.
Will reinstalling Firefox fix SEC_ERROR_BAD_SIGNATURE?
Reinstalling Firefox alone may not fix the error because the certificate database and profile settings are stored separately from the Firefox installation files and are not removed during a standard uninstall. To fully reset Firefox's certificate data, use the built-in 'Refresh Firefox' option (found at about:support) or manually delete the cert9.db file from your Firefox profile folder before reinstalling. If the issue is caused by your antivirus, network, or system clock, reinstalling Firefox will not help.

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