Are you talking about the home page? https://support.mozilla.org/en-US/kb/how-to-set-the-home-page Or the search engine? Type '''about:addons'''<enter> in the address bar to open your Add-ons Manager&#46; Hot key; '''(<Control> ''[Mac=<Command>]'' <Shift> A) ''' In the Add-ons Manager, on the left, select '''Extensions&#46; ''' Remove “ Bing “ '''Anything&#46; ''' Also remove SafeSearch, SearchAssist Incognito, FileConverter Addon, SearchLock, DiscreteSearch, WebSearch, Findwide Search Engine, securedsearch Now do the same in the computer’s '''Programs Folder&#46; ''' '''Windows:''' Start > Control Panel > Uninstall Programs&#46; '''Mac:''' Open the '''Applications''' folder&#46; '''Linux:''' Check your user manual&#46;

You may have to start Firefox in Safe Mode to be able to disable the extension that is the culprit. *https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode