Unable to import a certificate into the Authorities tab of Certificate Manager. I was able to import the certificate until I upgraded from Firefox v47 to v50

My company has a proxy server that is inspecting the HTTPS traffic and when I try to use Firefox to browse to an external secure site I am getting an error code: SEC_ERROR_UNKNOWN_ISSUER. I have tried going into Options>Advanced>Certificates>View Certificates>Authorities and using the Import button to import the certificate from our proxy server but nothing happens. I am able to go through the Downloading Certificate gui and don't receive any error messages but the list of certificate authorities never updates. I did not have this issue when I was using Firefox v47, but when I automatically updated to version 50.1 the certificate I imported was missing from the list and it doesn't show on the list when I go through the Import button. I have tried renaming the cert8.db file and that did not resolve my issue and I tried uninstalling Firefox and reinstalling with the latest version and that didn't resolve the issue.