Suppose we have the xhr 'POST' request that returns 'redirect' status code. In that case browser is sending additional xhr 'GET' by the given URL. I am not sure who is doing that call chain: browser itself or js library(using MooTools).
The problem is that the second 'GET' request is not recognized as xhr by the server: It doesn't have "X-Requested-With" header contains "XMLHttpRequest"
The problem appears only on Firefox, but not on Webkit. So, believe it is not related to js library bug.
Does anyone have ideas how to fix it?