That's... interesting.

 Issue 630877  has been merged into this issue.

So what happens here is that we have one callsite (ResourceFetcher::resourceForStaticData) that calls Platform::parseDataURL - which rejects/fails data URLs with an "unknown" MIME-type. Because of the isolation of SVGs embedded as images the load will be deferred, so no "regular" load will be attempted.
When loading the same thing outside of "<img> context" (like for the 'C' case in the test) Platform::parseDataURL will fail for the same reason - however a "regular" load will be initiated and succeed... because loading unrecognized MIME-type data is apparently not a problem if done asynchronously.

Putting this on the Loading Team table.

What's the desired behavior here? Should we be accepting the invalid mime types or rejecting them?

+Yoav, who is working on making data uris load asynchronously. No clue if that would affect logic here though.

> Should we be accepting the invalid mime types or rejecting them?

Yes =P. More seriously though, Gecko appears to "accept" it. (Could be worth checking other browsers too.) On the ImageResource/ImageDecoder-side we essentially ignore the MIME type (w/ exception for image/svg+xml) and always look at the image signature anyway.

> ...making data uris load asynchronously. ... if that would affect logic here though.

Well, data URLs w/ unrecognized MIME-types apparently always load async already =). For the "<img> context" we can't load data URLs async (which is part of the reason this fails), because of a number of assumptions higher in the stack about when an image is complete. That being said though, I don't think that would affect the logic here. (I.e if all data URL loads are async, this bug would be fixed.) Maybe that'd mean we wouldn't need to parse the data URL three times before delivering the data though =).

(triager notes)
Waiting for feedback from yoav@

Seems like Safari is also displaying B, so seems like we should display it for compat reasons.

I'll take a look if the async data URI change makes any difference here and report back.
 

It doesn't seem like async data URI loading is solving this issue. B still doesn't display with the patch applied.

 Issue 450894  has been merged into this issue.

triager assigning this to yoav@

 Issue 786031  has been merged into this issue.

Hey, coming in from  Issue 786031  here:

FWIW, it seems like some older versions of Illustrator and Photoshop would export SVG files with the bad mime type. I spoke with the designer who provided a bad SVG file to me (which caused me to open the issue in the first place), and after re-exporting the file with the latest version of AI, that it correctly had the "image/png" instead of "img/png" mime type. The designer's previous exports (generated about 2 months ago) had the faulty mime type, which might explain why its cropping up all the sudden.

Sorry about the broken links in the issue description, the hosting provider went out of business 😧  Well at least the attachments are there.

 Issue 797551  has been merged into this issue.

 Issue 811097  has been merged into this issue.

 Issue 813732  has been merged into this issue.