In rare cases when opening images, firefox refuses to display those with the error message: "This image cannot be displayed because it contains errors". While I do believe that those image files have errors, Firefox still should display the image as good as possible. Chrome and IE display the image just fine. IMO informing the user that the image contains errors is ok, but firefox should still do it's best at presenting the image.

This image is WebP format, depending on bug 1294490.

Follow-up: Apparently IE also has issues opening the sample I have uploaded. Strangely enough when opening it from the the original source URL (https://s.kaskus.id/r540x540/images/2017/04/13/1185794_20170413062122.JPG) IE has no issues at all.

The website appears to be sending different data depending on the browser used. It sends a jpg file if I use safari, but sends webp if I use chrome or firefox. I've seen a bug like this before, it was caused by the web server using an old version of an extension that has a bug.

(In reply to nucrap from comment #2) > Follow-up: Apparently IE also has issues opening the sample I have uploaded. > Strangely enough when opening it from the the original source URL > (https://s.kaskus.id/r540x540/images/2017/04/13/1185794_20170413062122.JPG) > IE has no issues at all. If I click on this link from the bug the network panel of dev tools tells me I get a 403 forbidden response and the image does not display. If I press enter in the url bar the image displays and I get 200 ok. So the server is also looking at the referer header.

Do we have a webcompat bug on webservers mistakenly sending webp to firefox?

tnikkel -- there's been a few. See the bug deps/blockers of Bug 856375 and <https://github.com/webcompat/web-bugs/labels/type-webp>. Most concerning is probably that an older versions of mod_pagespeed sent WebP to Fennec (https://github.com/pagespeed/mod_pagespeed/issues/1160).