appendChild

I read the recent quote on the Mozilla site, from the appendChild page
https://developer.mozilla.org/en/DOM/element.appendChild

############

Note: Starting in Firefox 3.1, you can no longer use this method to append 
script elements that retrieve their code from anything other than chrome: 
URLs.

############

I have been searching trying to find changelogs or discussion on this 
proposed change in Firefox. Unless I am misunderstanding the note on the 
Mozilla documentation page for appendChild, we will no longer be able to 
append a <script> element in the following manner:

        var script = document.createElement('script');
        script.type = 'text/javascript';
        script.src = 'test.js';
        document.getElementsByTagName('head')[0].appendChild(script);

Other browsers will allow DOM manipulation using these methods, so I 
question why is this change being incorporated in Firefox?