--- a/browser/themes/windows/browser.css
+++ b/browser/themes/windows/browser.css
@@ -121,24 +121,28 @@
       color: hsl(240,9%,98%);
     }
 
     /* Always show full-height tab separators on tabs with borders. */
     .tabbrowser-tab:not(:-moz-lwtheme)::before {
       border-image: none !important;
     }
 
-    /* Show the tabs toolbar background color inside tabs on Win 7. */
-    .tab-background:not(:-moz-lwtheme):not([selected=true]) {
+    /* Show border on tabs with background colors and
+     * show the tabs toolbar background color inside tabs. */
+    .tabbrowser-tab:not(:-moz-lwtheme) {
       background-color: hsl(235,33%,19%) !important;
+      border-top: 1px solid var(--tabs-border);
+      background-clip: padding-box;
     }
 
-    /* Show border on tabs with background colors in Windows 7. */
+    /* The top border on top of the tab background is replaced
+     * by the slightly transparent outside tabs-border. */
     .tab-background:not(:-moz-lwtheme) {
-      border-top: 1px solid var(--tabs-border);
+      border-top-style: none !important;
     }
   }
 }
 
 @media (-moz-windows-compositor: 0),
        (-moz-windows-default-theme: 0) {
   /* Please keep the menu text colors in this media block in sync with
    * compacttheme.css, minus the :not(:-moz-lwtheme) condition - see Bug 1165718.

--- a/browser/themes/windows/compacttheme.css
+++ b/browser/themes/windows/compacttheme.css
@@ -71,24 +71,28 @@
     }
   }
 
   /* Always show full-height tab separators on tabs with borders. */
   .tabbrowser-tab::before {
     border-image: none !important;
   }
 
-  /* Show the tabs toolbar background color inside tabs on Win 7. */
-  .tab-background:not([selected=true]) {
+  /* Show border on tabs with background colors and
+   * show the tabs toolbar background color inside tabs. */
+  .tabbrowser-tab {
     background-color: var(--chrome-background-color) !important;
+    border-top: 1px solid var(--tabs-border);
+    background-clip: padding-box;
   }
 
-  /* Show border on tabs with background colors in Windows 7. */
+  /* The top border on top of the tab background is replaced
+   * by the slightly transparent outside tabs-border. */
   .tab-background {
-    border-top: 1px solid var(--tabs-border);
+    border-top-style: none !important;
   }
 
   /* Use default window colors when in non-maximized mode */
   #tabbrowser-tabs,
   #TabsToolbar,
   #browser-panel,
   #titlebar-content {
     background: transparent;