--- a/mail/themes/osx/mail/messageHeader.css
+++ b/mail/themes/osx/mail/messageHeader.css
@@ -401,19 +401,21 @@ mail-emailaddress[selected="true"] .emai
     tweak the bottom to blend in more w/ the menu */
   cursor: pointer;
   color: HighlightText;
   background: linear-gradient(#6bb0fa, #167bff);
   border-bottom-left-radius: 0;
   border-bottom-right-radius: 0;
 }
 
-.emailDisplayButton:-moz-system-metric(mac-graphite-theme):hover,
-mail-emailaddress[selected="true"] .emailDisplayButton:-moz-system-metric(mac-graphite-theme) {
-  background: linear-gradient(#b1b1b6, #929297);
+@media (-moz-mac-graphite-theme) {
+  .emailDisplayButton:hover,
+  mail-emailaddress[selected="true"] .emailDisplayButton {
+    background: linear-gradient(#b1b1b6, #929297);
+  }
 }
 
 /* this is for the comma in between email addresses */
 .emailSeparator {
   margin-inline-start: -5px; /* squeeze it inside the bubble, by the star */
 }
 
 .emailDisplayButton:focus {

--- a/mail/themes/windows/mail/quickFilterBar.css
+++ b/mail/themes/windows/mail/quickFilterBar.css
@@ -3,18 +3,20 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 @import url("chrome://messenger/content/quickFilterBar.css");
 
 #quick-filter-bar-expando {
   border-bottom: 1px solid ThreeDShadow;
 }
 
-#qfb-filter-label:-moz-system-metric(windows-default-theme) {
-  color: GrayText;
+@media (-moz-windows-default-theme) {
+  #qfb-filter-label {
+    color: GrayText;
+  }
 }
 
 @media (-moz-os-version: windows-win7) {
   #qfb-qs-textbox {
     margin-top: 4px;
     margin-bottom: 4px;
   }
 }
@@ -39,19 +41,21 @@
 }
 
 #quick-filter-bar-tab-bar,
 #quick-filter-bar-filter-text-bar {
   margin-top: -2px;
   padding: 2px;
 }
 
-#quick-filter-bar-filter-text-bar:not(:-moz-system-metric(windows-default-theme)) {
-  padding-top: 3px;
-  padding-bottom: 3px;
+@media (-moz-windows-default-theme: 0) {
+  #quick-filter-bar-filter-text-bar {
+    padding-top: 3px;
+    padding-bottom: 3px;
+  }
 }
 
 /* :::: Filter Buttons :::: */
 
 #quick-filter-bar toolbarbutton {
   min-height: 19px;
   border: 1px solid transparent;
   padding: 2px 3px;