Does Firefox 4 not allow you to append script tags with external/local sources?

Question

Hello,
I am trying to use JSONP to append a <script> tag with an external source (and local)... The page I am trying to append is a valid JSON file, and the script worked fine in Firefox 3, and still works fine in Safari 5 and Internet Explorer 8... So it leads me to believe that Firefox 4 has closed the security hole that allowed me to do this.
The code I am using is:
$.jsonp({
url: "http://localhost/All.json",
callback: "callback",
success: function(data) {
alert("Success");
complete: function(xOptions, textStatus) {
alert("Complete");
error: function(xOptions, textStatus) {
// This will be called in case of error no matter the callback name
});

Answer 1

When debugging with Firebug it says this inbetween the <script> and </script> tags:
Failed to load source for: http://localhost/All.json?_1300977243502=