What instructions did you use to make it part of the search engine?

Why won't the DuckDuckGo search engine extension added in Firefox show in my search engine list?

https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox

Note that on most locales DDG should be one of the default search engines. Do you see this search engine listed on the "Help -> More Troubleshooting Information" (about:support) page ?

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.