Hi ! Even though Yahoo Search is a legitimate search engine, you may be dealing with search.yahoo.com redirect virus, malware that you of course will want to get rid of. Go to the 3-bar menu (or 'Tools') => Addons => Extensions and look for any unfamiliar or suspicious looking extensions, like e.g. : SafeSearch Incognito SearchAssist Incognito Search for Fire Fox 1.6 SafeSearch ch SafeSearch net Converter.onesearch org File Convertor and Search Addon Findwide Search Engine 1.7 When you find any : remove them. Do the same in Windows Control Panel. However : most malware will be 'hiding' somewhere , so let's run malware scans : Further information can be found in this article : https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no Run most or all of the listed malware scanners. They all work differently - what one program doesn't pick up, the other might. Also see : https://malwaretips.com/blogs/remove-us-search-yahoo-com/