diff --git a/browser/themes/windows/browser.css b/browser/themes/windows/browser.css
index 007aec91e089a1d2df20235890b268b820b0a529..ac0592cbcec62ffefb58b491dff48749852f2d88 100644
--- a/browser/themes/windows/browser.css
+++ b/browser/themes/windows/browser.css
@@ -31,7 +31,6 @@
     /* stylelint-disable-next-line media-query-no-invalid */
     @media -moz-pref("widget.windows.mica.toplevel-backdrop", 2) {
       /* For acrylic, do the same we do for popups to guarantee some contrast */
-      background-color: light-dark(rgba(255, 255, 255, .6), rgba(0, 0, 0, .6));
     }
   }