You may see the following error message when attempting to access a router's configuration page:

Your certificate contains the same serial number as another certificate issued by the certificate authority. Please get a new certificate containing a unique serial number. (Error code: sec_error_reused_issuer_and_serial)

This article describes the cause of this problem and how to work around it.

Causes

Older routers will sometimes improperly regenerate their security certificates instead of keeping the same one for the life of the device. If you have added a permanent security exception for your router, and if this regeneration is done improperly, Firefox will detect the change as a possible attack.

Solution

The long term solution is to contact your hardware vendor and see if updates are available for your device which fix this problem.

Workaround

If you are confident that no attack has occurred, you can work around the problem by deleting your old exception and using temporary exceptions for subsequent visits to the page:

To delete your old exception:

1. At the top of the Firefox windowOn the menu bar, click on the ToolsFirefoxEdit menu, and select Options...Preferences....
2. Select the Advanced panel.
3. Click on the Encryption tab.
4. Click View Certificates to open the Certificate Manager window.
5. In the Certificate Manager window click on the Servers tab.
6. Click on the item that corresponds to the site that generates the error and press Delete....
7. Click OK when prompted to delete the exception.
8. Click OK close the Certificate Manager window.
9. Click OKClose the preferences window.

To add a temporary exception to allow access to the page:

1. When you go to the page, you will be presented with an error. Click on the Or you can add an exception... link at the bottom of the error.
2. Click on Add Exception... to open the Add Security Exception window.
3. Click Get Certificate to fill in the Certificate Status section of the Add Security Exception window.
4. Click to un-check the Permanently store this exception.
   
   
   
5. Click Confirm Security Exception to close the Add Security Exception window.

The page will load.