Firefox for Windows, macOS, Linux and mobile versions for iOS/iPadOS, Android are web browsers. The company Mozilla does not have a search engine of their own. A search engine is DuckDuckGo.com, Google.com, Bing.com etc. The default search engine in most Firefox locales for desktop is Google ex: google.com/google.ca etc. If you do not want youtube.com links to come up in Google search results then In your Google search box you can add '''-site:youtube.com''' after your search terms. You can also go to Google Advanced Search page to customize search also.