This is a certificate conflict message. Actually firefox collects certificates and compare all incoming certificates. If these certificates match but come from different sources Firefox throws the certificate conflict message like “Secure Connection Failed”.
Most of the time, controller are installed with the same certificate during production. So when for the first time when you will access the controller, the browser will install this certificate in local certificate list. In case you access any other controller which have the same certificate installed but the source is different, there will be a conflict. It has been noticed that this issue comes only with Firefox and not with IE. The factory installed certificate on the WLC can be find at MANAGEMENT-->HTTP-->CURRENT CERTIFICATE.
Fixing this issue is pretty simple. After you configure your WLC with an IP address, go to MANAGEMENT-->HTTP and click on regenerate certificate. Once we regenerate the certificate, it will generate a unique certificate with latest validity date. Then reboot the controller for the certificate to take effect. Below is an example of regenerated certificate.
Relevant bug:There is a Bug filed related to this issue and has been fixed.