--- a/devtools/client/themes/widgets.css
+++ b/devtools/client/themes/widgets.css
@@ -343,55 +343,73 @@
 }
 
 .theme-light .breadcrumbs-widget-item:not([checked]):hover label {
   color: black;
 }
 
 /* Firebug theme support for breadcrumbs widget. */
 
+.theme-firebug #breadcrumb-separator-normal {
+  background: url(images/firebug/breadcrumbs-divider.svg);
+  width: 5px;
+  height: 7px;
+}
+
 .theme-firebug .breadcrumbs-widget-item {
-  margin-inline-start: 10px;
-  margin-inline-end: 1px;
+  margin-left: 1px;
+  margin-right: 5px;
   background-image: none;
   border: 1px solid transparent;
   color: #141414;
   border-radius: 2px;
   min-width: 0;
   min-height: 0;
   padding: 0;
   font-size: var(--theme-toolbar-font-size);
 }
 
+.theme-firebug .breadcrumbs-widget-item:-moz-locale-dir(rtl) {
+  margin-left: 5px;
+  margin-right: 1px;
+}
+
 .theme-firebug .breadcrumbs-widget-item:hover {
   border-color: rgba(0, 0, 0, 0.2);
   background: transparent linear-gradient(
               rgba(255, 255, 255, 0.4),
               rgba(255, 255, 255, 0.2)) no-repeat;
   box-shadow: 1px 1px 1px rgba(255, 255, 255, 0.6) inset,
               0 0 1px rgba(255, 255, 255, 0.6) inset,
               0 0 2px rgba(0, 0, 0, 0.05);
 }
 
 .theme-firebug .breadcrumbs-widget-item > .button-box {
   padding-left: 0;
   padding-right: 0;
 }
 
-.theme-firebug .breadcrumbs-widget-item:first-child {
-  margin: 0;
+.theme-firebug .breadcrumbs-widget-item:not(:first-child):-moz-locale-dir(ltr)::before,
+.theme-firebug .breadcrumbs-widget-item:not(:first-child):-moz-locale-dir(rtl)::after {
+  content: "";
+  display: inline-block;
+  background: -moz-element(#breadcrumb-separator-normal) no-repeat center center;
+  position: relative;
+  width: 5px;
+  height: 7px;
 }
 
-.theme-firebug .breadcrumbs-widget-item:not(:first-child)::before {
-  content: url(chrome://devtools/skin/images/firebug/breadcrumbs-divider.svg);
-  position: relative;
+.theme-firebug .breadcrumbs-widget-item:-moz-locale-dir(ltr)::before {
   left: -3px;
-  margin: 0 0 0 -5px;
-  padding: 0;
-  width: 5px;
+  margin: 0 0 0 -6px;
+}
+
+.theme-firebug .breadcrumbs-widget-item:-moz-locale-dir(rtl)::after {
+  right: -7px;
+  margin: 0 -3px 0 0;
 }
 
 /* Breadcrumbs Separators (reset selection styles) */
 .theme-firebug .breadcrumbs-widget-item[checked],
 .theme-firebug .breadcrumbs-widget-item[checked] .breadcrumbs-widget-item-id,
 .theme-firebug .breadcrumbs-widget-item[checked] .breadcrumbs-widget-item-tag,
 .theme-firebug .breadcrumbs-widget-item[checked] .breadcrumbs-widget-item-pseudo-classes,
 .theme-firebug .breadcrumbs-widget-item[checked] .breadcrumbs-widget-item-classes {