Duckduckgo Onion Lite search does not work properly in safest when added as a search engine

Duckduckgo Onion Lite search appends "html" to the end of every search query in "safest" when added as a search engine option in the browser.

I added the search engine by going to "about:config" in the url bar and adding the "preference" "browser.urlbar.update2.engineAliasRefresh" and setting it to "true". After that I can go to "about:preferences#search" in the url, go to the bottom of the page and then press the "add" button to add "https://duckduckgogg42xjoc72x3sjasowoarfbgcmvfimaftt6twagswzczad.onion/lite/?q=%s"

The issue is only reproducible when tor browser is set to "safest". It does not reproduce in "standard" security level.

In testing, the issue was also reproducible on the safest security level when using the extensions https://addons.mozilla.org/en-US/firefox/addon/search-engines-helper/ and https://addons.mozilla.org/en-US/firefox/addon/add-custom-search-engine/

I spoke to duckduckgo and they said it was a browser issue and not their end.