--- a/devtools/server/actors/highlighters.css
+++ b/devtools/server/actors/highlighters.css
@@ -20,16 +20,18 @@
   Content CSS applying to the html element impact the highlighters.
   To avoid that, possible cases have been set to initial.
   */
   text-transform: initial;
   text-indent: initial;
   letter-spacing: initial;
   word-spacing: initial;
   color: initial;
+  direction: initial;
+  writing-mode: initial;
 }
 
 :-moz-native-anonymous .highlighter-container {
   --highlighter-guide-color: #08c;
   --highlighter-content-color: #87ceeb;
   --highlighter-bubble-text-color: hsl(216, 33%, 97%);
   --highlighter-bubble-background-color: hsl(214, 13%, 24%);
   --highlighter-bubble-border-color: rgba(255, 255, 255, 0.2);