Use about:logo again r=Mano

toolkit/content/about.xhtml

@@ -61,7 +61,7 @@
 <div id="aboutPageContainer">
   <div id="aboutLogoContainer">
     <a href="http://www.mozilla.org/">
-      <img src="chrome://branding/content/about.png" alt="&brandShortName;"/>
+      <img src="about:logo" alt="&brandShortName;"/>
 #expand <p id="version">&about.version; __MOZ_APP_VERSION__</p>
     </a>
   </div>