Index: drupalforfirebug.module
===================================================================
--- drupalforfirebug.module	(revision 710)
+++ drupalforfirebug.module	(working copy)
@@ -264,6 +264,17 @@
   if (!user_access('Access Firebug Debug')) {
     return;
   }
+  if (function_exists('drupal_get_http_header')) {
+    $header = drupal_get_http_header('content-type');
+    if ($header) {
+      $formats = array('xml', 'javascript', 'json', 'plain', 'image', 'application', 'csv', 'x-comma-separated-values');
+      foreach ($formats as $format) {
+        if (strstr($header, $format)) {
+          return;
+        }
+      }
+    }
+  }
   $output = '<div style="display: none" id="drupalforfirebug_general">';
   $output .= '<fieldset>';
   $output .= '<legend>' . t('Drupal for Firebug General Messages') . '</legend>';