I was gently doing some ajax black voodoo when I came upon this obscure-ish error in my firebug console:
Error: uncaught exception: [Exception... "Component returned failure code: 0x805e000a [nsIXMLHttpRequest.open]" nsresult: 0x805e000a (<unknown>)"
What the fuck I though. And then after some (useless) firefox rebooting, I decided to ask the all-mighty Google.
No shit, he said, I know what you are talking about, and thou shall find more informations at this place, and to point me to this thread, where you can read the following:
AdBlock Plus was killing it HAH!
And then I disabled AdBlock Plus, and exactly as the writings told, it worked.