Now that Content Alignment CSS properties were upgrade to the new CSS Box Alignment specification is time now to implement their functionality in Grid Layout. This bug is about the justify-content support, which means that we should be able to align the grid container along the inline/row axis supporting different writing modes and flow directions.
I finally implemented support for both properties in bug #145520, so I'll close this one. *** This bug has been marked as a duplicate of bug 145520 ***