diff --git a/browser/themes/osx/devedition.css b/browser/themes/osx/devedition.css
index 09de57ce28ab..3905c24625c8 100644
--- a/browser/themes/osx/devedition.css
+++ b/browser/themes/osx/devedition.css
@@ -32,6 +32,16 @@
   margin-top: 6px;
 }
 
+/* In private windows, the #titlebar-content is higher because of the
+ * private browsing indicator. With the margin-top the titlebar buttons
+ * align to the top correctly in that case, but only if we don't stretch
+ * the box they're in because the container is too high, so we override
+ * the default alignment value (stretch).
+ */
+#main-window[tabsintitlebar] > #titlebar > #titlebar-content > #titlebar-buttonbox-container {
+  -moz-box-align: start;
+}
+
 /* Square back and forward buttons.  Need !important on these because there
    are a lot of more specific selectors sprinkled around elsewhere for changing
    background / shadows for different states */