Great idea. Lossless WebP is generally a superior alternative to Png (except it cannot handle HQs beyond 16k on a side), but when you get served a webp on a web site, there is a 95% chance it is just a Jpg that has gone through another round of lossy compression, a different type, at a lower bit rate = worse quality (fewer fine details).

In an ideal world, the digital master would be encoded as both Jpg/Png and Jxl, and the browser would have an option built in to preference one format over the other. JpegXl is the best new format. Jpeg2000 was decent but I don't think any browsers support it, and it even has a lossless format.

Unfortunately, this extension only works on some sites. Some are still sending me Webp,oravif (less often) and even twice I got a Jpegxl (I wish to force jpeg from these bossy CDNs that are enforcing inferior formats upon me).

It used to work pretty fine but for some time it doesn't work at all. Still all webp images are accepted.

It's worked great for the most part for years now but seems to not work on some sites for whatever reasons. Updated, and I tried changing settings back and forth but some sites it just does not work on. Imgur for example, it wont work if I'm on the main page, but if I go ahead and click on an image and then try it , it works. odd. Seem to be finding more sites it just does not work on lately, but it still works on most at least.

Doesn't seem to work. I've selected strip webp and avif, but both the developer console and https://www.whatismybrowser.com/detect/what-http-headers-is-my-browser-sending say I'm still sending webp and avif in the Accept header.

Edit: Strangely, toggling the "Run in Private Windows" to "Allow" and back to "Don't allow" (which is my desired setting) fixed the issue, even though I always ran the tests in normal browsing instead of private browsing. I'm unable to replicate this for a proper bug report, but just a FYI for others facing similar issues.

TLDR: This addon genuinly tries to do what it promises but Firefox defaults + servers = useless addon.
The addon does something, but it's not resulting in refusal of webp images.

By clicking the "W" button on the toolbar, the sent "Accept" headers either include or don't include "image/webp", but it's of no use at all if the default following is "*/*".

It's possible to change the value of the "image.http.accept" key in "about:config" to (for example)
image/png,image/jpeg;q=1
but this addon will then not be able to change this value anymore.

Furthermore, websites such as Youtube (Google in general) just plain refuse to offer anything but webp, even if Firefox does not indicate support for it in the "Accept" header. You may need to fool these websites in assuming you're using an old browser by changing or emptying the "general.useragent.override" key.

Edited at 14/01/2024: changed rating 2»4; addon is not to blame for servers ignoring user preferences, as indicated in response by addon author.