Firefox web browser keeps track of the websites you visit in your browsing sessions. It stores you browsing history, active logins,form and search history, website cookies and cache, site settings and offline website data. But you can easily clear and delete all Firefox history data.
Delete Firefox History:
Open your Firefox web browser and click the menu button to open the Application Menu panel and click History
Then click the Clear recent history.
Select the time range and other preferences and click Clear Now button.
That’s it. To clear everything check all options and set the time range to Everything.