XML isn't loading in FF


I am having trouble loading XML content from Firefox. At this very moment I have Safari and Firefox open: Safari works every time, and firefox is unpredictable. When I run the code from within Flash CS3 it works 100% of the time.

The XML contains the names of folders within a directory, and I’m turning that information into a menu.

Here is the AS3 code:

var myXMLLoader:URLLoader = new URLLoader();
myXMLLoader.load(new URLRequest("http://*.com/xml/categories.php"));

myXMLLoader.addEventListener(Event.COMPLETE, processMenuXML);
function processMenuXML(e:Event):void {
    myMenuXML=new XML(e.target.data);
    my_sections = myMenuXML.section;
    my_sections_total = my_sections.length();

categories.php returns this code:

<?xml version="1.0" encoding="UTF-8"?>
<section name="ANIMALS"></section>
<section name="LANDSCAPES"></section>
<section name="MISC"></section>
<section name="PORTRAITS"></section>
<section name="STREET"></section>
<section name="TRAVEL"></section>

I have tried it with and without the XML Version/Encoding line, and I have also linked directly to a .xml file and neither has made a difference.

Any ideas?