1. Open FireFox
  2. Click on
  3. Once the Options Windows opens, click on 'Find in Options' and type in 'Certificates'
  4. Click on 'Select one automatically'
  5. Click on 'View Certificates'
  6. Once the Certificate Manager window has opened, ensure that that the Authorities tab is selected and then click on Import
  7. Find and select the certificate file to import, click on Open
      1. note the certificate name may be different, but the extension will always be a .cer.
  8. Ensure that both tick boxes are checked and click on OK.
  9. Click on OK in the Certificates Manager window
  10. Close Firefox and relaunch.