diff --git a/userChrome.css b/userChrome.css
index 8e7b10f..491eefd 100644
--- a/userChrome.css
+++ b/userChrome.css
@@ -178,6 +178,10 @@
   }
 
   /** Selected Tab - Color like toolbar ***************************************/
+  :root:not(:-moz-lwtheme) {
+    /* Fix for windows's system default theme. Using --toolbar-bgcolor fallback */
+    --tab-selected-bgcolor: unset !important; /* Original: rgb(255,255,255); */
+  }
 #tabbrowser-tabs:not([movingtab]) > #tabbrowser-arrowscrollbox > .tabbrowser-tab > .tab-stack > .tab-background[selected="true"]:-moz-lwtheme {
     /* Original: linear-gradient(var(--lwt-selected-tab-background-color, transparent), var(--lwt-selected-tab-background-color, transparent)), linear-gradient(var(--toolbar-bgcolor), var(--toolbar-bgcolor)), var(--lwt-header-image, none)
  */