diff --git a/toolkit/themes/osx/global/toolbar.css b/toolkit/themes/osx/global/toolbar.css
index b912f12d5d9e..04e90887121c 100644
--- a/toolkit/themes/osx/global/toolbar.css
+++ b/toolkit/themes/osx/global/toolbar.css
@@ -14,7 +14,7 @@ menubar:-moz-lwtheme,
 toolbar:-moz-lwtheme {
   -moz-appearance: none;
   background: none;
-  border-style: none;
+  border-color: transparent;
 }
 
 menubar {
diff --git a/toolkit/themes/windows/global/menu.css b/toolkit/themes/windows/global/menu.css
index ebfdd977d587..aa7cdfb9f532 100644
--- a/toolkit/themes/windows/global/menu.css
+++ b/toolkit/themes/windows/global/menu.css
@@ -127,7 +127,7 @@ menubar > menu[_moz-menuactive="true"][open="true"] {
 
 menubar > menu:-moz-lwtheme {
   -moz-appearance: none;
-  border-style: none;
+  border-color: transparent;
 }
 
 menubar > menu:-moz-lwtheme:not([disabled="true"]) {
diff --git a/toolkit/themes/windows/global/toolbar.css b/toolkit/themes/windows/global/toolbar.css
index 991592d2ab22..68327e780191 100644
--- a/toolkit/themes/windows/global/toolbar.css
+++ b/toolkit/themes/windows/global/toolbar.css
@@ -43,7 +43,7 @@ toolbox:-moz-lwtheme,
 toolbar:-moz-lwtheme {
   -moz-appearance: none;
   background: none;
-  border-style: none;
+  border-color: transparent;
 }
 
 /* ::::: toolbar decorations ::::: */