@aljoscha I'm sorry to be the bearer of bad news, but I just realized that the rule about integer keys being numerically ordered only applies to ints, not integers.

> obj = {}
{}
> obj[Math.pow(2, 44)] = 1
1
> obj[Math.pow(2, 43)] = 2
2
> obj[Math.pow(2, 31)] = 3
3
> obj
{
  '2147483648': 3,
  '17592186044416': 1,
  '8796093022208': 2
}

but it gets worse... it's actually only integers from 0 - 0xfffffffe!
the 2^32-2! 0xffffffff, 4294967295 is the first integer key treated as a string.

However, I confirmed this in both firefox and chrome, weird but seems to be intended.