I noticed that URLs like the following https://ucarecdn.com/608d722c-cc33-41e8-95a9-94ea7c1af95e/-/format/auto/ return PNG/JPEG instead of WebP. Ucarecdn (Uploadcare) is a service that provides uploads/storage/delivery. It optimizes images on-the-fly, and the "format/auto" operation should serve a WebP version of the image if the client supports this format. It checks the "accept" header for the "image/webp" value, and it it's presented, converts the image to WebP and serves it. However, I can see the "accept" header's value doesn't contain "image/webp" when I request the image. Here are the request's headers: Host: ucarecdn.com User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:67.0) Gecko/20100101 Firefox/67.0 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br DNT: 1 Connection: keep-alive Upgrade-Insecure-Requests: 1 If I request WebP explicitly, I get a WebP version, and it is displayed in the browser correctly https://ucarecdn.com/608d722c-cc33-41e8-95a9-94ea7c1af95e/-/format/webp/ In browser config I have: image.http.accept; image/webp,*/* image.webp.enabled; true