If you hover the tile then you will see the three dot menu. If you open this menu then you will see "Delete from History", if this doesn't work then try "Dismiss". The latter stores this URL as a hash in browser.newtabpage.blocked on the <b>about:config</b> page and best is not to dismiss a lot of sites as this will decrease the value of the pref and you have no way to tell what websites you have dismissed. You can also Edit this tile and pin a different website to that tile. *https://support.mozilla.org/en-US/kb/customize-new-tab-page *https://support.mozilla.org/en-US/kb/hide-or-display-content-new-tab ---- Changes made manually on the about:newtab page are stored in prefs that you can find on the <b>about:config</b> page. *browser.newtabpage.pinned => websites pinned to a tile *browser.newtabpage.blocked => websites removed by clicking the X (Dismiss) button in a tile