Auge works on certain browsers and doesn't on others for some strange reason.

- When I try to open it in Firefox, it wants to force me to download the image. Google says it may be because the image was saved as a webp instead of a real png, and Firefox doesn't support webp yet. It could also be something to do with the MIME type (which I don't know much about).

I'd suggest going back to whatever program you made the overlay in, and double checking the settings you used when you saved/exported the image.

This could certainly explain why it isn't working on some browsers/mobile devices. It wasn't me who made the custom overlaying but i know the artist who did.

If you just redownload the image using Firefox or use an addon in Chrome that will allow you to save files as the format of your choice it should be fine.

webp is Google making problems because Google.