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Guide to Fix SEC_ERROR_REUSED_ISSUER_AND_SERIAL Error Mozilla Firefox

If you’ve landed on this article, there’s a high chance that you’re seeing the Mozilla Firefox Error message sec_error_reused_issuer_and_serial, also called Secure Connection Failed, whenever you try to access the router configuration page.

Why Does the Mozilla Firefox Error sec_error_reused_issuer_and_serial Occur?

Usually, old routers are the culprit. They improperly regenerate their security certificates rather than keeping the same one for the device. Unless a permanent security exception is added to the router and regeneration wasn’t proper, Firefox will detect and show this change as a possible attack. For instance, this SSL connection error can occur to the web-based GUI, after an upgrade of the wireless controller.

How to Solve the Secure Connection Failed Mozilla Firefox Error?

If you’re confident enough that no attack has occurred, try the following.

1. Check SSL Settings of Mozilla Firefox

In the Address Bar, type about:config and hit Enter.

Click on the “Accept the Risk and Continue” button while selecting the checkbox “Warn me when I attempt to access these preferences.

Now, in the search bar, type security.ssl.enable_ocsp_stapling like:
By default, the value is true, double click on it and change it to false:
After completing the above-mentioned steps, try to reload the page that displayed this error. If you still see the error message, try another solution.

2. Check Proxy Settings in Mozilla Firefox

If you’ve configured your computer through Proxy to access the Internet, then you may face this Secure Connection Failed Mozilla Firefox Error: sec_error_reused_issuer_and_serial.

To solve:

Click on the Tools menu and select Options from the Mozilla Firefox menu bar.

In your latest Mozilla Firefox (Ver. 71.0), scroll down to Network Settings and click the Settings button.
A pop-up named Connection Settings will open and if you find the Manual proxy configuration option enabled, it means your PC is configured to use a manual proxy server.
So, you have to recognize whether all the protocol fields – HTTP Proxy, SSL Proxy, FTP Proxy, and SOCKS Host, have been entered correctly. If not, modify and click on OK. On the other hand, if the Manual proxy configuration is not enabled like above, then ignore this page and contact the person who handles your network connection.

3. Check Your Site’s SSL Installation/Configuration

An incorrectly installed SSL/TLS Certificate might be the reason for the Mozilla Firefox error message, Secure Connection Failed, along with error code: sec_error_reused_issuer_and_serial. So, it’s recommended to check your installed SSL’s configuration using free tools such as SSL Checker.


To sum it up, Secure Connection Failed error occurs due to old routers or improper proxy settings. If you’re facing this issue and the given steps don’t work, do not be disappointed. If the website does not open, you can try opening another site or you can try another browser. If the problem persists, you can contact the person who operates your network and you’ll get the solution.

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