How to add the No-AI version of Duck Duck Go as default search engine in Firefox for Mac:
* Choose "Preferences" in Firefox's main menu
* Click on "Search" in the left column
* Scroll down past Search Subjects and press "Add" button
* For search engine name, enter a name like "No-AI Duck Duck Go"
* For URL, enter https://noai.duckduckgo.com/?q=%s (make sure there's https:// at the front)
* Click on "Add Engine"
* Scroll up the page to "Default search engine" and pick the new name from the menu