--- a/toolkit/themes/windows/global/textbox.css
+++ b/toolkit/themes/windows/global/textbox.css
@@ -26,17 +26,17 @@ html|*.textbox-textarea {
   margin: 0px !important;
   border: none !important;
   padding: 0px 1px !important;
   background-color: inherit;
   color: inherit;
   font: inherit;
 }
 
-@media (-moz-windows-default-theme) {
+@media (-moz-windows-default-theme) and (-moz-os-version: windows-win7) {
   textbox html|*.textbox-input::placeholder {
     font-style: italic;
   }
 }
 
 .textbox-contextmenu {
   cursor: default;
 }