Oh, you're the dev of diffui? It's completely off-topic, but I've notice that RMB -> Download image will download an .png but it's actually a .webp and it can cause issues (e.g. file explorer doesn't show thumbnail correctly).

Indeed I am! Also nice catch - should have a fix up in the next hour. Hit me up with any other reqs - j@diffui.ai

Edit: confirmed that the download should be fixed now - should be properly a png now.