User blog comment:HankGuideDude/Hia-logue 5-01: The Prism & Upsilon expansion/@comment-1416754-20190405021710/@comment-2012328-20190407233711

Found out about this too from the link in the Starbox - FANDOM migrated the WEBP format around 2 years ago and I guess the browsers - Firefox particularly - had recently adapted to showing WEBP files, hence the lowish quality.

Managed to trick the browser to load the images normally using about:config.