--- a/devtools/client/themes/netmonitor.css
+++ b/devtools/client/themes/netmonitor.css
@@ -499,21 +499,23 @@
 /* Size Column */
 .theme-firebug .requests-menu-subitem.requests-menu-size {
   text-align: end;
   padding-inline-end: 4px;
 }
 
 /* Network request details */
 
-#details-pane-toggle {
+#details-pane-toggle:-moz-locale-dir(ltr),
+#details-pane-toggle.pane-collapsed:-moz-locale-dir(rtl) {
   list-style-image: var(--theme-pane-collapse-image);
 }
 
-#details-pane-toggle.pane-collapsed {
+#details-pane-toggle.pane-collapsed:-moz-locale-dir(ltr),
+#details-pane-toggle:-moz-locale-dir(rtl) {
   list-style-image: var(--theme-pane-expand-image);
 }
 
 /* Network request details tabpanels */
 
 .tabpanel-content {
   background-color: var(--theme-sidebar-background);
 }