DuckDuck is a private search engine that you can use as an alternative to Google. This search engine promises not to use your personal information for a commercial purpose like Google did.
Some web browsers -- including Firefox -- have added DuckDuckGo on their search engine list, but not set as the default search engine yet. Instead, the majority of web browsers still use Google as the default search engine, including Firefox.
Not everyone loves using Google, especially those who care about privacy. Google tracks your search activities for an advertising purpose. It's no secret.
By default, if you type any keyword on the address bar of Firefox, you will be presented with the search results of Google's search engine. But you can change it if you want. Firefox gives you a freedom to choose your favorite search engine as the default search engine.
To set DuckDuckGo as the default search engine on Firefox, you can go to the Preferences menu which you can find under the Edit menu.
On the Preferences page, select the Search menu on the left panel and go the Default Search Engine section. Select DuckDuckGo.
By now, if you type any keyword on the address bar of Firefox you will be presented the search results of DuckDuckGo instead of Google.