Don't allow content scripts to execute on file:// urls....

chrome/common/extensions/docs/static/content_scripts.html

 <div id="pageData-title" class="pageData">Content Scripts</div>
 <div id="pageData-showTOC" class="pageData">true</div>
 
 <p>
 Content scripts are JavaScript files that run in the context of web pages.
 By using the standard
 <a href="http://www.w3.org/TR/DOM-Level-2-HTML/">Document
 Object Model</a> (DOM),
 they can read details of the web pages the browser visits,
 or make changes to them.
@@ skipping 22 matching lines @@
   </li>
   <li>
     Use variables or functions defined by their extension's pages
   </li>
   <li>
     Use variables or functions defined by web pages or by other content scripts
   </li>
   <li>
     Make cross-site XMLHttpRequests
   </li>
+  <li>
+    Execute on file:// urls.
+  </li>
 </ul>
 
 <p>
 These limitations aren't as bad as they sound.
 Content scripts can <em>indirectly</em> use the chrome.* APIs,
 get access to extension data,
 and request extension actions
 by exchanging <a href="messaging.html">messages</a>
 with their parent extension.
 Content scripts can also
@@ skipping 148 matching lines @@
 just like you would any other URL,
 as the following code shows.
 </p>
 
 
 <pre>
 <em>//Code for displaying &lt;extensionDir>/images/myimage.png:</em>
 var imgURL = <b>chrome.extension.getURL("images/myimage.png")</b>;
 document.getElementById("someImage").src = imgURL;
 </pre>