Thanks Dropa but this did not solve my problem. My issue is specific to DuckDuckGo. I tried adding the DuckDuckGo engine from "Find More Search Engines" in Settings. DuckDuckGo was offered as an option and I installed the add-in. When I went back to the FF Settings it did not appear in the options. I restarted FF with the same result. I even restarted my Mac. No joy. I tried the other solutions in the link you sent but they did not work either. This is the settings menu after i added DuckDuckGo add-in from the find more search engines.

Thanks. I have emailed them.

Hi WDMc, DuckDuckGo is pre-installed with Firefox. We'll need some more info about your Firefox setup. Could you please follow the instructions in the following video to provide your troubleshooting information: https://youtu.be/8wKSowxEcbw

If clearing the "Restore Default Search Engines" on the "Settings -> Search" page doesn't work, try to rename/remove search.json.mozlz4 in the Firefox profile folder with Firefox closed to rebuild the search engines registry.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Firefox will rebuild search.json.mozlz4 from the built-in search engines.