Mozilla Firefox keeps a list of all web pages you have visited.
The Browsing History tool allows you to view, delete and manage the list of visited pages.
You can select (check) one or several web page addresses and then press the Delete button in order to delete the pages. Bellow the page list you have the Select (all, none and invert) button, which allow you to select all, clear the selection completely, and invert the current selection.