You can customize your new tab page to remove the top sites. When on the new tab page, click the settings icon (the gear symbol). Then disable the "Top sites" in the preferences. Now no top sites will show up

Note that best is to avoid using Dismiss. When you click Dismiss then a hash value of this website is stored in a pref on the about:config page that can grow quite large over time.

It is better to use 'remove from history' if you do not want a specific page to appear on the Firefox Home page. Alternatively you can pin links to each of the tiles via the three dot menu to prevent any pages getting added.

• 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 about:config page.

• browser.newtabpage.pinned => websites pinned to a tile
• browser.newtabpage.blocked => websites removed by clicking the X (Dismiss) button in a tile

Wouldn't deleting from history also delete the website from my browsing history?

Yes, using delete will remove this page from the history. Firefox will always fill tiles from pages you have recently visited, so it is either remove a file from history or pin sites to a tile to prevent unwanted website in a tile or disable the top sites section or use Private Browsing mode.

Did you check the browser.newtabpage.blocked pref on the about:config page ?

Yes I did, and nothing came up.

Desktop

On desktop, simply click the circle-shaped Ellipsis icon that shows up whenever you hover over a listed item. On the context menu that shows up, click Dismiss to make the thumbnail disappear.

However, it may still show up after a while. If you don't want that, click Delete From History instead to delete the thumbnail permanently.

Mobile

On mobile, it’s just a matter of performing a long-press on any unwanted item and selecting either Remove or Delete From History — the former hides listings temporarily, while the latter removes them permanently.

Note: Clearing your browsing data also removes all recently accessed sites from Top Sites and Highlights. However, any bookmarked pages displayed within Highlights aren't affected.

So, in other words... No, there isn't.

Top Site tiles will always be filled by visited websites. Like I wrote above, you can either pin websites or links to each of the tiles or simply hide this section if you do not want to use it. If pinning isn't working for some reason then there is a problem with the pref that stores the pinned sites.

• browser.newtabpage.pinned => websites pinned to a tile
• browser.newtabpage.blocked => websites removed by clicking the X (Dismiss) button in a tile