It should remain a 'bug'. That's an invalid URL in the IMG tag and should be treated as such. The problem is some browsers 'helpfully' fix it and designers don't know they're writing invalid HTML.

Browsers like Internet Explorer 'fix' it so designers never know. Browsers like Firefox show it as properly broken so designers fix their mistakes. That's why it's always important to test your site in a proper browser.

I know you have 'bug' in quotes, but man, you know perfectly well that's not a bug and it would be complete silliness to allow that.

Is it though? I know standards are important, but what does it really cost a browser maker to be able to resolve paths with backslashes? Similarly, is it really that big of a deal to support background-position-x and y? The prime example of something should have been a spec from the beginning.

That road of good intentions leads to maintenance problems like HTML quirks mode and security issues (especially when allowing invalid URLs).

nope, doesn't work in Chromium 36.

Nor in Opera 12.

I stand corrected!

What's supposed to happen?

There's an invalid URI within the IMG starting with http:\\ instead of http://. A mistake a beginner designer who's used to Windows directories would make. Some browsers like IE helpfully 'fix' this mistake and accept it so the beginner designers have no idea they're writing broken code. Other browsers like Firefox interpret it as written and show it as broken.

Hmm, with Chrome in W8 it shows an image, So I didn't see anything wrong...

The wrong slash has been used in the URL. It's supposed to be a broken image.