Firefox is a web browser while Yahoo is a search engine like google.com, duckduckgo.com bing.com are. The desktop Firefox web browser has not come with Yahoo as a search engine default for over 6 1/2 years now so whatever you are seeing is not from Mozilla nor does Firefox come with it as you can see in [/forums/contributors/712925] Perhaps an Extension you have installed or updated in Firefox recently has added a Yahoo search engine. Or perhaps it has changed your Homepage settings in Firefox to be say yahoo.com or such. https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox https://support.mozilla.org/en-US/kb/how-to-set-the-home-page https://support.mozilla.org/en-US/kb/extension-changed-my-new-tab-page https://support.mozilla.org/en-US/kb/wrong-home-page-opens-when-i-start-firefox-how-fix