It seems that Firefox saves our .webp transforms of .jpgs as files with the .jpg file extension. (unlike Chrome which automatically renames the filename to .webp). This leads to 'broken' files for some people.
File upstream bugreport ?
Maybe try automatically adding `Content-Disposition: inline; filename*="filename.webp"` on such files, seems we strip that header right now (unintentionally ?)
`curl -v -O -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8" "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Bonette.jpg/320px-Bonette.jpg"`
```
< HTTP/2 200
< date: Thu, 04 Jun 2020 12:48:50 GMT
< content-type: image/jpeg
< content-length: 10814
< x-object-meta-sha1base36: ahk541f5c9nejdk8fj1uofq9r085p7q
< content-disposition: inline;filename*=UTF-8''Bonette.jpg
< last-modified: Thu, 30 Mar 2017 18:48:33 GMT
< etag: 13b9ebe4294ac964665f5eff7391d4b8
< x-timestamp: 1490899712.93189
< server: ATS/8.0.7
< age: 74344
< x-cache: cp3059 hit, cp3065 hit/2543
< x-cache-status: hit-front
< server-timing: cache;desc="hit-front"
< strict-transport-security: max-age=106384710; includeSubDomains; preload
< x-client-ip: 82.197.207.202
< access-control-allow-origin: *
< access-control-expose-headers: Age, Date, Content-Length, Content-Range, X-Content-Duration, X-Cache
< timing-allow-origin: *
< accept-ranges: bytes
```
`curl -v -O -H "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8" "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Bonette.jpg/320px-Bonette.jpg"`
```
< HTTP/2 200
< date: Fri, 05 Jun 2020 00:28:05 GMT
< content-type: image/webp
< content-length: 11832
< last-modified: Fri, 26 Jul 2019 12:20:19 GMT
< etag: 64858bb14ad22a72049c432862316152
< x-timestamp: 1564143618.12390
< server: ATS/8.0.7
< age: 32455
< x-cache: cp3057 miss, cp3065 hit/601
< x-cache-status: hit-front
< server-timing: cache;desc="hit-front"
< strict-transport-security: max-age=106384710; includeSubDomains; preload
< x-client-ip: 82.197.207.202
< access-control-allow-origin: *
< access-control-expose-headers: Age, Date, Content-Length, Content-Range, X-Content-Duration, X-Cache
< timing-allow-origin: *
< accept-ranges: bytes
```