--- a/browser/base/content/test/performance/browser_windowopen_reflows.js
+++ b/browser/base/content/test/performance/browser_windowopen_reflows.js
@@ -63,22 +63,16 @@ if (Services.appinfo.OS == "WINNT") {
 
     {
       stack: [
         "handleEvent@chrome://browser/content/tabbrowser.xml",
         "inferFromText@chrome://browser/content/browser.js",
         "handleEvent@chrome://browser/content/browser.js",
       ],
     },
-
-    {
-      stack: [
-        "handleEvent@chrome://browser/content/tabbrowser.xml",
-      ],
-    }
   );
 }
 
 if (Services.appinfo.OS == "WINNT" || Services.appinfo.OS == "Darwin") {
   EXPECTED_REFLOWS.push(
     {
       stack: [
         "verticalMargins@chrome://browser/content/browser-tabsintitlebar.js",
@@ -96,27 +90,32 @@ if (Services.appinfo.OS == "WINNT" || Se
         "init@chrome://browser/content/browser-tabsintitlebar.js",
         "handleEvent@chrome://browser/content/tabbrowser.xml",
       ],
       times: 4, // This number should only ever go down - never up.
     },
   );
 }
 
+// Windows Vista, 7 or 8
+if (navigator.userAgent.indexOf("Windows NT 6") != -1) {
+  EXPECTED_REFLOWS.push(
+    {
+      stack: [
+        "handleEvent@chrome://browser/content/tabbrowser.xml",
+      ],
+    },
+  );
+}
+
 /*
  * This test ensures that there are no unexpected
  * uninterruptible reflows when opening new windows.
  */
 add_task(async function() {
-  const IS_WIN8 = (navigator.userAgent.indexOf("Windows NT 6.2") != -1);
-  if (IS_WIN8) {
-    ok(true, "Skipping this test because of perma-failures on Windows 8 x64 (bug 1381521)");
-    return;
-  }
-
   // Flushing all caches helps to ensure that we get consistent
   // behaviour when opening a new window, even if windows have been
   // opened in previous tests.
   Services.obs.notifyObservers(null, "startupcache-invalidate");
   Services.obs.notifyObservers(null, "chrome-flush-skin-caches");
   Services.obs.notifyObservers(null, "chrome-flush-caches");
 
   let win = OpenBrowserWindow();