Don’t “Accept” image/webp ：This extension removes image/webp from the list of formats Firefox tells sites that it accepts. That should discourage many servers from replacing JPEG and PNG images with WebP images. (But some may send webP anyway; it isn't blocked.)..
Don’t “Accept” image/webp 更新
Don’t “Accept” image/webp 简介
Firefox usually sends websites an indicator that it can handle webP-format images, and this may encourage sites to send images in webP formats. This extension strips out that indicator from requests (more specifically, the Accept header) so sites are more likely to send JPEG and PNG format images.
(1) Although broad permission is needed for this extension to modify the Accept header, no data is read from requests, responses, or web pages.
(2) This extension monitors and edits request headers using the onBeforeSendHeaders API. There is a possibility of a conflict with other extensions that use the same API, which can lead to inconsistent results for both extensions.
Note: since Firefox 68, users cannot directly edit the network.http.accept.default preference, so if you found an old solution of removing image/webp from that preference, you’ve found the right new workaround.