Hi ! Even though Yahoo is a legitimate search engine, you may be dealing with search.yahoo.com Redirect virus, malware that you will of course want to get rid of. Go to the 3-bar menu (or 'Tools') => Addons => Extensions and look for '''any unfamiliar or suspicious looking extensions'''. When you find any : remove them. Do the same in your system's 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/yahoo-toolbar-removal/ And : https://www.pcrisk.com/removal-guides/8835-search-yahoo-com-redirect