--- a/layout/style/TopLevelImageDocument.css
+++ b/layout/style/TopLevelImageDocument.css
@@ -3,16 +3,20 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 /*
   This CSS stylesheet defines the rules to be applied to ImageDocuments that
   are top level (e.g. not iframes).
 */
 
+html:-moz-locale-dir(rtl) {
+  direction: rtl;
+}
+
 @media not print {
   body {
     margin: 0;
   }
 
   img {
     text-align: center;
     position: absolute;