diff --git a/__tests__/list.test.scss b/__tests__/list.test.scss
index 85d920d..82e570f 100644
--- a/__tests__/list.test.scss
+++ b/__tests__/list.test.scss
@@ -21,6 +21,22 @@ $dupList: (ab cd efgh efgh efgh ijk);
   }
 }
 
+@include test-module("Remove at list using list [fn]") {
+  @include test("simple") {
+    @include assert-equal(
+      list.remove-list($simpleList, ("cd" "efgh")),
+      (ab ijk)
+    );
+  }
+
+  @include test("duplicate") {
+    @include assert-equal(
+      list.remove-list($dupList, ("cd" "efgh")),
+      (ab ijk)
+    );
+  }
+}
+
 @include test-module("Convert to str [fn]") {
   @include test("simple") {
     @include assert-equal(
diff --git a/__tests__/native_menu.test.scss b/__tests__/native_menu.test.scss
index 5a766a8..38d96d4 100644
--- a/__tests__/native_menu.test.scss
+++ b/__tests__/native_menu.test.scss
@@ -1,8 +1,11 @@
 @use "true" as *;
 @use "example" as *;
 @use "../src/utils/native_menu";
+@use "../src/utils/os" as OS;
+
+@include test-module("Native Menu Option - ESR [mix]") {
+  @include OS.ESR-MODE;
 
-@include test-module("Native Menu Option [mix]") {
   @include test("simple") {
     @include assert {
       @include output {
@@ -117,3 +120,121 @@
     }
   }
 }
+
+@include test-module("Native Menu Option - Standard [mix]") {
+  @include OS.STANDARD-MODE;
+
+  @include test("simple") {
+    @include assert {
+      @include output {
+        @include native_menu.NativeToolkitMenu {
+          @include example;
+        }
+        @include native_menu.NativeMenuPopup {
+          @include example;
+        }
+      }
+      @include expect {
+        @supports -moz-bool-pref("widget.macos.native-context-menus") or -moz-bool-pref("widget.gtk.native-context-menus") {
+          @include example;
+        }
+        menupopup:is(#historyMenuPopup, #bookmarksMenuPopup),
+        menupopup:not([placespopup="true"]) {
+          @include example;
+        }
+      }
+    }
+  }
+  @include test("native menu - with windows media") {
+    @include assert {
+      @include output {
+        @include native_menu.NativeMenu(true) {
+          @include example;
+        }
+        @include native_menu.NonNativeMenu(true) {
+          @include example;
+        }
+        @include native_menu.WinNativeMenu(true) {
+          @include example;
+        }
+        @include native_menu.WinNonNativeMenu(true) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media not (-moz-windows-non-native-menus) {
+          @media (-moz-platform: windows) {
+            @include example;
+          }
+        }
+        @supports not -moz-bool-pref("userChrome.theme.non_native_menu") {
+          @media (-moz-gtk-csd-available) {
+            @include example;
+          }
+        }
+        @media (-moz-windows-non-native-menus) {
+          @media (-moz-platform: windows) {
+            @include example;
+          }
+        }
+        @supports -moz-bool-pref("userChrome.theme.non_native_menu") {
+          @media (-moz-gtk-csd-available) {
+            @include example;
+          }
+        }
+        @media not (-moz-windows-non-native-menus) {
+          @media (-moz-platform: windows) {
+            @include example;
+          }
+        }
+        @media (-moz-windows-non-native-menus) {
+          @media (-moz-platform: windows) {
+            @include example;
+          }
+        }
+      }
+    }
+  }
+  @include test("native menu - without windows media") {
+    @include assert {
+      @include output {
+        @include native_menu.NativeMenu {
+          @include example;
+        }
+        @include native_menu.NonNativeMenu {
+          @include example;
+        }
+        @include native_menu.WinNativeMenu {
+          @include example;
+        }
+        @include native_menu.WinNonNativeMenu {
+          @include example;
+        }
+      }
+      @include expect {
+        @media not (-moz-windows-non-native-menus) {
+          @include example;
+        }
+        @supports not -moz-bool-pref("userChrome.theme.non_native_menu") {
+          @media (-moz-gtk-csd-available) {
+            @include example;
+          }
+        }
+        @media (-moz-windows-non-native-menus) {
+          @include example;
+        }
+        @supports -moz-bool-pref("userChrome.theme.non_native_menu") {
+          @media (-moz-gtk-csd-available) {
+            @include example;
+          }
+        }
+        @media not (-moz-windows-non-native-menus) {
+          @include example;
+        }
+        @media (-moz-windows-non-native-menus) {
+          @include example;
+        }
+      }
+    }
+  }
+}
diff --git a/__tests__/os.test.scss b/__tests__/os.test.scss
index 8e66f06..e42d95b 100644
--- a/__tests__/os.test.scss
+++ b/__tests__/os.test.scss
@@ -2,8 +2,9 @@
 @use "example" as *;
 @use "../src/utils/os" as *;
 
-// TODO: Need more tests..
-@include test-module("Create OS related media [mix]") {
+@include test-module("Create OS related media - ESR [mix]") {
+  @include ESR-MODE;
+
   @include test("win7") {
     @include assert {
       @include output {
@@ -145,3 +146,145 @@
     }
   }
 }
+
+@include test-module("Create OS related media - Standard [mix]") {
+  @include STANDARD-MODE;
+
+  @include test("win7") {
+    @include assert {
+      @include output {
+        @include OS($win7) {
+          @include example;
+        }
+      }
+      @include expect {
+        // IGNORE
+      }
+    }
+  }
+
+  @include test("win8") {
+    @include assert {
+      @include output {
+        @include OS($win8) {
+          @include example;
+        }
+      }
+      @include expect {
+        // IGNORE
+      }
+    }
+  }
+
+  @include test("win10") {
+    @include assert {
+      @include output {
+        @include OS($win10) {
+          @include example;
+        }
+      }
+      @include expect {
+        // AS Windows
+        @media (-moz-platform: windows) {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("linux") {
+    @include assert {
+      @include output {
+        @include OS($linux) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media (-moz-gtk-csd-available) {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("mac") {
+    @include assert {
+      @include output {
+        @include OS($mac) {
+          @include example;
+        }
+      }
+      @include expect {
+        @supports -moz-bool-pref("layout.css.osx-font-smoothing.enabled") {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("bigsur") {
+    @include assert {
+      @include output {
+        @include OS($bigsur) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media (-moz-mac-big-sur-theme: 0) {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("win") {
+    @include assert {
+      @include output {
+        @include OS($win) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media (-moz-platform: windows) {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("all os - win7, win8, win10, mac, bigsur, linux") {
+    @include assert {
+      @include output {
+        @include OS($win7, $win8, $win10, $mac, $bigsur, $linux) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media  (-moz-platform: windows), (-moz-mac-big-sur-theme: 0), (-moz-gtk-csd-available) {
+          @include example;
+        }
+        @supports -moz-bool-pref("layout.css.osx-font-smoothing.enabled") {
+          @include example;
+        }
+      }
+    }
+  }
+
+  @include test("all os - win, mac, bigsur, linux") {
+    @include assert {
+      @include output {
+        @include OS($win, $mac, $bigsur, $linux) {
+          @include example;
+        }
+      }
+      @include expect {
+        @media (-moz-platform: windows), (-moz-mac-big-sur-theme: 0), (-moz-gtk-csd-available) {
+          @include example;
+        }
+        @supports -moz-bool-pref("layout.css.osx-font-smoothing.enabled") {
+          @include example;
+        }
+      }
+    }
+  }
+}
diff --git a/src/leptonChrome.scss b/src/leptonChrome.scss
index ea1aca0..41e9938 100644
--- a/src/leptonChrome.scss
+++ b/src/leptonChrome.scss
@@ -16,6 +16,7 @@
 @namespace xul "http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul";
 @namespace html "http://www.w3.org/1999/xhtml";
 
+@include ESR-MODE;
 /** Default Theme - Contrast **************************************************/
 @include Option("userChrome.theme.built_in_contrast") {
   @import "theme/built_in";
diff --git a/src/leptonContent.scss b/src/leptonContent.scss
index 0ef3035..7eaa1a7 100644
--- a/src/leptonContent.scss
+++ b/src/leptonContent.scss
@@ -11,6 +11,7 @@
 @namespace xul url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
 @namespace html url("http://www.w3.org/1999/xhtml");
 
+@include ESR-MODE;
 /** Compatibility *************************************************************/
 @import "contents/compatibility";
 
diff --git a/src/utils/_list.scss b/src/utils/_list.scss
index 933f923..6a6f4ee 100644
--- a/src/utils/_list.scss
+++ b/src/utils/_list.scss
@@ -4,17 +4,25 @@
 @function remove($list, $value, $recursive: false) {
   $result: ();
 
-  @for $i from 1 through length($list) {
-    @if type-of(nth($list, $i)) == list and $recursive {
-      $result: append($result, remove(nth($list, $i), $value, $recursive));
-    } @else if nth($list, $i) != $value {
-      $result: append($result, nth($list, $i));
+  @each $item in $list {
+    @if type-of($item) == list and $recursive {
+      $result: append($result, remove($item, $value, $recursive));
+    } @else if $item != $value {
+      $result: append($result, $item);
     }
   }
 
   @return $result;
 }
 
+@function remove-list($list, $removeList, $recursive: false) {
+  @each $removeItem in $removeList {
+    $list: remove($list, $removeItem, $recursive);
+  }
+
+  @return $list;
+}
+
 @function to-string($list, $glue: '', $is-nested: false) {
   $result: null;
 
diff --git a/src/utils/_os.scss b/src/utils/_os.scss
index 7c2ca6c..45edcb5 100644
--- a/src/utils/_os.scss
+++ b/src/utils/_os.scss
@@ -31,13 +31,14 @@ $_win-media: (
   $_win-media: map.set($_win-media, $_win-key, $result-template);
 }
 
+$_moz-platform-windows: list.nth($_win-template, 2);
 @function _win-only-result() {
   $result-template: ();
 
   @each $_win-value in map.values($_win-media) {
     $result-template: list.append($result-template, list.nth($_win-value, 1));
   }
-  @return list.append($result-template, list.nth($_win-template, 2))
+  @return list.append($result-template, $_moz-platform-windows)
 }
 
 $_win-media: map.merge(
@@ -54,7 +55,24 @@ $_os-media: map.merge(
 );
 
 //== Mixin =====================================================================
+$osESR: false !default;
+
+@mixin ESR-MODE() {
+  $osESR: true !global;
+}
+
+@mixin STANDARD-MODE() {
+  $osESR: false !global;
+}
+
 @mixin OS($osNames...) {
+  $_os-media: $_os-media; // as local
+  @if not $osESR {
+    $osNames: list-utils.remove-list($osNames, ($win7 $win8));
+    $_os-media: map.set($_os-media, $win10, $_moz-platform-windows);
+    $_os-media: map.set($_os-media, $win, $_moz-platform-windows);
+  }
+
   $osMedias: ();
   @each $osName in $osNames {
     $osMedia: map.get($_os-media, $osName);