my browser is firefox and in right hand corner is the search bar for google, only its not google any more, but Yahoo, how did that come about, if you understand me.
You did something, maybe without realising it, which changed your default search engine. Just change it back: https://www.searchenginejournal.com/change-your-default-search-engine-in-firefox-google-chrome-ie-original/24378/
had to go into the bars that look like a hamburger, because i had lost my google search bar, does that make sense, whoever told me click on hamburger go to customise and drag the option across to search bar.
Depending on make and version of operating system, just go into the place where you uninstall applications that you no longer want, find everything called Yahoo Search / Yahoo Toolbar etc and uninstall.