I've implement the Rich Text Editor with the Custom Image Browser plugin  (http://developer.yahoo.com/yui/examples/editor/imagebrowser_editor.html)

I want to disable the url from being editable once they selected a image.

I copied the code as requested:

myEditor.on('afterOpenWindow', function() {
    //When the window opens, disable the url of the image so they can't change it
    var url = Dom.get('insertimage_url');
    if (url) {
        url.disabled = true;
    }
}, myEditor, true);

But the url is still enable even when trying the example at

http://developer.yahoo.com/yui/examples/editor/imagebrowser_editor.html