Are that websites that you have visited or websites that Firefox shows by default (directory tiles)/ *https://support.mozilla.org/kb/how-do-tiles-work-firefox You can change the order of the boxes on the about:newtab page and drag an item to a different tile to pin it to that position or you can remove a website by clicking the close X to block that URL. You can drag a bookmark or history item from the sidebar and drop it in a tile on the about:newtab page to pin this item and have your own favorites sites present. Changes made manually on the about:newtab page are stored in prefs that you can find on the about:config page. *browser.newtabpage.pinned stores websites that you have pinned to a tile. *browser.newtabpage.blocked stores websites that you have removed by clicking the X button in a tile.