diff -r 000000000000 -r 6474c204b198 browser/base/content/test/general/browser_private_no_prompt.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/test/general/browser_private_no_prompt.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,12 @@
+function test() {
+  waitForExplicitFinish();
+  var privateWin = OpenBrowserWindow({private: true});
+
+  whenDelayedStartupFinished(privateWin, function () {
+    privateWin.BrowserOpenTab();
+    privateWin.BrowserTryToCloseWindow();
+    ok(true, "didn't prompt");
+
+    executeSoon(finish);
+  });
+}