diff --git a/css/leptonContent.css b/css/leptonContent.css
index 5049a6e..02ccc11 100644
--- a/css/leptonContent.css
+++ b/css/leptonContent.css
@@ -2887,6 +2887,7 @@
 @supports -moz-bool-pref("userChrome.rounding.square_menupopup") {
   @-moz-document url-prefix("about:"), url-prefix("chrome://")
   {
+    panel,
     menupopup {
       --panel-border-radius: 0 !important;
     }
diff --git a/src/contents/_rounding.scss b/src/contents/_rounding.scss
index 28beaed..7b59098 100644
--- a/src/contents/_rounding.scss
+++ b/src/contents/_rounding.scss
@@ -113,6 +113,7 @@
 
 @include Option("userChrome.rounding.square_menupopup") {
   @include moz-document(url-prefix "about:", url-prefix "chrome://") {
+    panel,
     menupopup {
       --panel-border-radius: 0 !important;
     }