I figure you are talking about firefox internet browser? To clear history,open firefox, go to tools>Clear Recent History, and select how long (everything reccommended). click clear, and your all set
If you mean that whenever you start to type in the Answer or Ask box above, and it automatically suggests the history of what you typed, the only probable way to get rid of it is by deleting all of...
If it hasn't been erased you could search all cookies and it will tell you what site the computer has been to. You could also locate at the top of the internet browser a section called 'history'....