Proposed target bug: Bug 1929151 Related bugs: 1993701, 1204850, 1409529
Suggested summary if a new bug is preferred:
Firefox resolves dimensionless SVG <img> to 0x0 inside width:fit-content parent when the img has width:100% and max-width
Suggested Bugzilla comment for Bug 1929151:
This looks like another reduced testcase for the same underlying issue, but affecting `width: fit-content` on the parent instead of `min-width` / `max-content` on the image itself.