title: file is being assigned a //# sourceMappingURL but already has one
body: <p>I just notice Firefox console outputs the following error for every single .js/.coffee file in my project (even the packages).</p>
  
  <pre><code>-file- is being assigned a //# sourceMappingURL, but already has one
  </code></pre>
  
  <p>Chrome's console doesn't show anything. I tried deleting all the .map files and clearing Firefox's cache but I'm still getting the errors.</p>