Clear search history on a Macbook on Mozilla Firefox?

For Gmail- when you first log in theres that bar where you type in your username and password but I want all the other past usernames to be erased. I already tried the TOOLS --%26gt; CLEAR PRIVATE DATA... and checked all the boxes but the past usernames that peple logged in with wont go awayClear search history on a Macbook on Mozilla Firefox?
Displays the History Sidebar, which keeps track of the sites you have visited. To change how many days a site should be remembered, select Tools %26gt; Options Edit %26gt; Preferences Firefox %26gt; Preferences and select the Privacy panel.





try this