1. Click the Firefox Menu.
2. Select and open “Options”.
3. Select the “Advanced” option and then the “Certificates” tab…
…then click View Certificates.
4. In the “Certificate Manager” panel, click the “Authorities” tab and select the target certificate, then click the Delete or Distrust button.
5 . In the “Delete or Distrust CA Certificates” panel, make sure the target certificate is the one you wish to delete, then click OK to remove it.