Creator here. I've restricted the access token for the data to only incoming traffic from that specific domain (tjukanovt.github.io), so maybe Firefox is doing something weird there. As if you can't access the tileset, you only get that blue ball.
Works for me with Firefox 102/Linux
Me too: Firefox 103, macOS. And I did turn off uBlock Origin.
The Planet is a blue ball if you point to Eastern Island