Each query in the Search History has a checkbox. Checked queries are deleted when you click on the Delete button. They are also deleted automatically when you issue a fresh query from the Query box. When queries are inserted in the Search History panel they are already checked and thus, if you do nothing, they go away when you issue the next query from the Query box. To retain a query in the Search History, clear its checkbox.
Search History queries are stored in local storage contolled by the Flash Player independently of your browser and are preserved when you leave noflail.com or close the browser. To delete all queries so that they are not seen by the next user of the computer, click on the Reset button in the orange top bar.
You can drag a query to a different position in the Search History, or drag it to the Query box to issue it again as a fresh query, producing a zero-result analysis or related queries as appropriate. Older versions of Noflail Search had a double-click feature. That feature has been removed.