Per http://www.mediawiki.org/wiki/Special:Code/MediaWiki/72349#c8904 and below, the resource loader outputs invalid CSS when it fails to determine the MIME type of the file it's embedding, resulting in CSS like url(data:;base64,....) , which is invalid and causes problems.

When the MIME type cannot be determined, we could try to guess based on the extension but we probably really should not embed the file at all.

Version: 1.17.x
Severity: enhancement