Replace DuckDuckGo with non-JS
In Security Settings -> Headers -> Alternative search engines
Please replace DuckDuckGo with the non-JS version:
[https://duckduckgo.com/html/]
Because the default one won't work when JS is disabled. And also if you use method POST it's better. There's no queries shown in the URL
Also are you planning to add any "alternative search engine" plugins? Especially this one:
[https://addons.mozilla.org/en-US/firefox/addon/duck-duck-go-html-search-plugi/]