--- theme.inc   2009-03-27 11:11:29.951768800 -0400
+++ theme.inc   2009-03-27 11:17:40.244867800 -0400
@@ -1752,7 +1752,19 @@
 function template_preprocess_page(&$variables) {
   // Add favicon
   if (theme_get_setting('toggle_favicon')) {
-    drupal_set_html_head('<link rel="shortcut icon" href="'. check_url(theme_get_setting('favicon')) .'" type="image/x-icon" />');
+    if ( strlen(theme_get_settings('favicon')) <= 4 ) {
+      $icontype = 'image/x-icon';
+    }
+    elseif ( strtolower(substr(theme_get_settings('favicon'),-4)) == '.png' ) {
+      $icontype = 'image/png';
+    }
+    elseif ( strtolower(substr(theme_get_settings('favicon'),-4)) == '.gif' ) {
+      $icontype = 'image/gif';
+    }
+    else {
+      $icontype = 'image/x-icon'; //'image/vnd.microsoft.icon' is official, but not widely supported.
+    }
+    drupal_set_html_head('<link rel="shortcut icon" href="'. check_url(theme_get_setting('favicon')) .'" type="' . $icontype . '" />');
   }

   global $theme;