mark Android Firefox as officially supported

docs/_includes/getting-started/browser-device-support.html

@@ -20,7 +20,7 @@
         <tr>
           <th>Android</th>
           <td class="text-success"><span class="glyphicon glyphicon-ok"></span> <span class="sr-only">Supported</span></td>
-          <td class="text-danger"><span class="glyphicon glyphicon-remove"></span> <span class="sr-only">Not Supported</span></td>
+          <td class="text-success"><span class="glyphicon glyphicon-ok"></span> <span class="sr-only">Supported</span></td>
           <td class="text-muted" rowspan="3" style="vertical-align: middle;">N/A</td>
           <td class="text-danger"><span class="glyphicon glyphicon-remove"></span> <span class="sr-only">Not Supported</span></td>
           <td class="text-muted">N/A</td>