This is one of those excellent addons that once you've tried it, you'll wish that you had known about it earlier.

It currently works on most sites although not all, since some sites will simply refuse to send you the original jpeg/png (or the image may not even exist in that format on their servers). In those cases you can use the author's other addon "Save webP as PNG or JPEG (Converter)" to convert to jpeg/png.

It has never broken any website for me or caused me any trouble so it's pretty easy to forget that you even have it installed. But at the same it has made saving pictures so much less annoying.

How can I tell it's working if I forget I even have it? Well whenever a site forces a webp file on me then the "Save webP as..." addon makes a popup appear asking me if I want to convert the file. Since installing this addon, I see that popup much MUCH less often so on those rare occasions where I do see this popup, I suddenly remember this addon and realize that it's been silently doing its job in the background for a while.

Thank you for the great addon jscher2000!

This is the best option. No conversions needed.

Simple and effective. It tells the server that you can't read webp formats so that web server sends you JPG or PNG. You can also tell it not to send avif files. I don't have a problem with webp/avif, but websites are recompressing lossy formats (JPG) to these new formats and that I don't like.

Saves me from needing to crop screenshots of webpages

thank you! webp drives me crazy on tumblr. finally back to the gifs! XD

Thank you Thank you Thank you!
webp might be nice to allow smaller images, but when I want to download them it's a pain. Almost no program knows how to handle webp images

Any chance you can make is work in FF mobile? pretty please

Fantastic. Works exactly as described so far, only issue I ran into is you have to restart firefox for it to work after installing, but this might be a thing with all addons.
Don't mind the 1-star reviews: some people just aren't very smart and they put the blame on the program rather than the user.

Worked perfectly. I have it turned off by default because, obviously, the new formats are better, but sometimes I need the older formats for compatibility.