Are there any major browsers that do not preserve insertion order in a JavaScript Object?

Question

Can I depend on the following code alerting b before a?

var x = {}
x['b'] = 1
x['a'] = 0
for(var i in x) {
    alert(i)
}

Answer 1

Are there any major browsers that do not preserve insertion order in a JavaScript Object?

At least one major browser did until recently (I think the V8 engine didn't preserve order).

Can I depend on the following code alerting b before a?

No. The spec says that there is no order.