--- a/devtools/client/framework/options-panel.css
+++ b/devtools/client/framework/options-panel.css
@@ -10,17 +10,21 @@
 }
 
 #options-panel {
   display: block;
 }
 
 .options-vertical-pane {
   display: inline;
-  float: inline-start;
+  float: left;
+}
+
+.options-vertical-pane:dir(rtl) {
+  float: right;
 }
 
 .options-vertical-pane {
   margin: 5px;
   width: calc(100%/3 - 10px);
   min-width: 320px;
   padding-inline-start: 5px;
   box-sizing: border-box;