This may be your problem; Firefox v52+ disables all plugins except for Flash [https://support.mozilla.org/en-US/kb/npapi-plugins Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work?] {web link} ------------------- [https://support.mozilla.org/en-US/kb/install-older-version-of-firefox?cache=no Install Older Version Of Firefox] {web link} Be sure to read everything here. If you still want to downgrade, look under; '''I still want to downgrade. ''' Click the '''Directory of other versions and languages''' link. Look for the directory of the version that you want. But, remember that '''old versions may have security issues. ''' You should also check out [https://www.mozilla.org/en-US/firefox/organizations/ Firefox; Extended Support Release] {web link} [https://www.mozilla.org/en-US/firefox/organizations/notes/ ESR Notes] [https://www.mozilla.org/en-US/firefox/organizations/system-requirements/ System Requirements]

Thank you Fred McD - do I understand correctly then that I will never be able to use Firefox in conjunction with Prizm again?

You can use the ESR version. Also, contact Prizm and have them talk to Mozilla.org (not this page).