Sorry about that, can you try this and let me know if you encounter the same error:

1) Open Preferences > Extensions and uninstall the DuckDuckGo extension if it's there
2) Safari > Quit Safari (make sure it closes completely)
3) Re-open safari and navigate to
4) Click 'Install' on the popup and try re-installing the extension
posted by brians Staff2 years and 4 months ago Link