--- a/browser/themes/osx/browser.css
+++ b/browser/themes/osx/browser.css
@@ -52,17 +52,24 @@
 }
 
 /** Begin titlebar **/
 
 #titlebar-buttonbox > .titlebar-button {
   display: none;
 }
 
-/* NB: these would be margin-inline-start/end if it wasn't for the fact that OS X
+/* Making the toolbox position:relative (browser.inc.css) occludes titlebar indicators
+ * if the toolbox has a background. Fix this by positioning the relevant elements, too: */
+#titlebar-secondary-buttonbox {
+  position: relative;
+  z-index: 1;
+}
+
+/* These would be margin-inline-start/end if it wasn't for the fact that OS X
  * doesn't reverse the order of the items in the titlebar in RTL mode. */
 .titlebar-placeholder[type="caption-buttons"],
 #titlebar-buttonbox {
   margin-left: 7px;
 }
 
 .titlebar-placeholder[type="fullscreen-button"],
 #titlebar-secondary-buttonbox {

--- a/browser/themes/windows/browser.css
+++ b/browser/themes/windows/browser.css
@@ -1094,16 +1094,19 @@ notification[value="translation"] {
 .private-browsing-indicator {
   display: none;
   pointer-events: none;
 }
 
 #private-browsing-indicator-titlebar {
   display: block;
   position: absolute;
+  /* Need to ensure this gets positioned on top of the position:relative #navigator-toolbox
+   * in case the dark/light themes give that item a background. */
+  z-index: 1;
 }
 
 #main-window[privatebrowsingmode=temporary][tabsintitlebar] #private-browsing-indicator-titlebar > .private-browsing-indicator {
   display: block;
 }
 
 #main-window[privatebrowsingmode=temporary]:-moz-any([inFullscreen],:not([tabsintitlebar])) #TabsToolbar > .private-browsing-indicator {
   display: -moz-box;