CKEditor Text Area Replacement Shows as Blank Area in Firefox 29

This is pretty straightforward, really.  I'm using v4.1.1, and the editor panel displays just fine in IE9 and Chrome 34, but I only see a blank area in Firefox 29.  I'm hoping it's just something simple that I'm doing wrong.

Here's the text area element on the page:

<textarea id="messageEditor" rows="20" cols="100"></textarea><br>

Here's the script that gets called after the page loads:

$(document).ready(
  function() {
   // Create the CKEditor instance.
   CKEDITOR.replace('messageEditor', {
    customConfig: '/app/scripts/message_editor_config.js',
    contentsCss: '/app/css/message_editor_contents.css',
    uiColor: '#14B8C4'
   });
  });
 

I'm seeing no errors in Firebug.  I would appreciate it very much if someone could point out what I'm doing wrong here.  Thanks.