The CSS Working Group just discussed [css-sizing-3] max-content contribution of replaced only-ar elements might be improvable, and agreed to the following:
RESOLVED: Specify Firefox's behavior
The full IRC log of that discussion
<dael> Topic: [css-sizing-3] max-content contribution of replaced only-ar elements might be improvable
<dael> github: https://github.com//issues/4218
<dael> fantasai: We triaged this last week. Case is we have some box which says I want width max-content
<dael> fantasai: Something inside it intrinsically sized with an aspect ratio and no size info
<dael> fantasai: No interop. Chrome is 0x0 as max content. Spec says use 300px width and ratio for height. Resolvable but arbitratry. FF uses initial containing block. That seems useful. We suggest spec FF behavior
<dael> astearns: Concerns?
<dael> astearns: Objections to Specify Firefox's behavior?
<dael> RESOLVED: Specify Firefox's behavior