Apparently, those exact images just can't render properly in Firefox and its forks.

Hello! If my Pokémon name list doesn't show any images, it's because of the volume of requests coming to the Pokémon TCG API (https://pokemontcg.io/). The owner has already been working on v3, but there is no ETA and I know some features will be paid. Some IPs have been banned from accessing the API for constantly maxing out rate limits.