The CSSWG just discussed "Indefiniteness when sizing grid tracks in a flexible flex item" https://github.com/w3c/csswg-drafts/issues/4852 There's a difference between implementations between Firefox & Chromium. The CSSWG clarify that Firefox is correct, and does what the spec says. Chromium has a bug. Presumably WebKit has the same bug. If we do, this should be fixed. See CSSWG issue + Chromium bug for details. Chromium bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1055258
*** This bug has been marked as a duplicate of bug 228149 ***