title: Could I make a Google Chrome extension for chrome pages (downloads, extensions etc)?
body: <p>I'd like to make a very simple extensions that slightly alters how the Downloads page looks. Changing the History page might be interesting too, but that's for later.</p>
  
  <p>Is there a way to do that?</p>
  
  <p>I tried making a <a href="http://code.google.com/chrome/extensions/content_scripts.html" rel="nofollow"><code>Content Script</code></a> extension, with <code>"chrome://downloads"</code> as <code>match</code> in <code>manifest.json</code>. Chrome won't allow that and responds with an error when packaging the extension.</p>
  
  <p><strong>Is there another simple way?</strong> It has to be simple, because changes would be simple, because all <code>chrome://</code> pages are built with HTML, JS and CSS.</p>
  
  <p><strong>edit</strong><br>
  After trying with background scripts a little...</p>
  
  <p>I can't get <code>chrome.tabs.executeScript</code> to work! I added in <code>background.html</code>:</p>
  
  <pre><code>chrome.browserAction.onClicked.addListener(function(tab) {
      alert(this.document.body.innerHTML);
      alert(chrome.tabs.executeScript(null, {
          code : "document.body.style.backgroundColor = 'red';"
      }));
  });
  </code></pre>
  
  <p>And I added this in <code>manifest.json</code> to add a (invisible) 'browser action button':</p>
  
  <pre><code>    ,"browser_action": {
  /*      "popup": "background.html",*/
          "name": "Alter page"
      }
  </code></pre>
  
  <p>The <code>onClicked</code> event fires both alerts (first is <code>background.html</code>'s body, second is <code>undefined</code>). But the code (a string with <code>document.body.style.backgroundColor = 'red';</code>) doesn't execute! And ofcourse there's no debugging for extensions like this =)</p>
  
  <p>Any tips anyone? I'm trying to get a hold of the tab's <code>window.document</code> (<strong>not</strong> <code>background.html</code>'s <code>window.document</code>!). An injected script (that's what <code>chrome.tabs.executeScript</code> is supposed to do) should do that.</p>
  
  <p><strong>PS</strong><br>
  I'm stealing from <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/browserAction/make_page_red/manifest.json?content-type=text/plain" rel="nofollow">make_page_red/manifest</a> and <a href="http://src.chromium.org/viewvc/chrome/trunk/src/chrome/common/extensions/docs/examples/api/browserAction/make_page_red/background.html?content-type=text/plain" rel="nofollow">make_page_red/background.html</a><br>
  The 'extension' I have so far: <a href="http://hotblocks.nl/js/downloads.rar" rel="nofollow">http://hotblocks.nl/js/downloads.rar</a></p>
  
  <p><strong>EDIT</strong><br>
  I found out what I want to achieve is possible with just CSS. I don't need to inject javascript. Does that make it easier? Does that make it possible? =)</p>