Maybe you have adware or even malware on the computer. It is normally very easy to change search engines from the searchbar, and that adjusts the search used from other things including the address bar, new tabs page and homepage * [[Use the Search bar in Firefox and manage search engines]] Remove any obvious unwanted toolbars using Firefox's addons page. lso check and remove any unwanted programs using Window Control panel. Then check for malware * [[Remove a toolbar that has taken over your Firefox search or home page]] * [[Troubleshoot Firefox issues caused by malware]] Note you should run multiple and up to date scanning tools.