It's secretly been there for probably a very long time because I stupidly never checked outside of Firefox. Interestingly, old Opera (with Presto) displays it the same as Chromia do today, so I'll have to reread the spec to see who's right. In any case it's a bit distressing that there's still such a big rendering difference a decade down the line.
I should probably just convert it to flexbox or grid instead.
