Yes, you need to get rid of a "tile" on the new tab page" that is associated with the game. This could take a few minutes.

After loading the new tab page and canceling whatever dialogs come up, zoom out so you can see the default 15 tiles that Firefox generates from your history. (For example, hold down Ctrl and tap the - key)

Then hopefully it will be obvious which tile is causing the problem and you can hover your mouse over it until an X appears at the upper right corner and click that to block this tile from appearing in the page.

Alternately, you can delete the history associated with that tile from the Library window. To launch that, either Ctrl+Shift+h or "Show All History". In the upper right corner, enter part of the title or address of the page to filter the list. When you find it, you can delete its history entries.

Do either of those methods work for you?

Is this about a tile on the about:newtab page?

If that is the case then you can click the X to remove (block) this item. You can also use "Forget About This Site" if you aren't interested in the website.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks and history and cookies and passwords and cache and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox