diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_586068-multi_window.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_586068-multi_window.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,66 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const PREF_RESTORE_ON_DEMAND = "browser.sessionstore.restore_on_demand";
+
+function test() {
+  TestRunner.run();
+}
+
+function runTests() {
+  Services.prefs.setBoolPref(PREF_RESTORE_ON_DEMAND, false);
+  registerCleanupFunction(function () {
+    Services.prefs.clearUserPref(PREF_RESTORE_ON_DEMAND);
+  });
+
+  // The first window will be put into the already open window and the second
+  // window will be opened with _openWindowWithState, which is the source of the problem.
+  let state = { windows: [
+    {
+      tabs: [
+        { entries: [{ url: "http://example.org#0" }], extData: { "uniq": r() } }
+      ],
+      selected: 1
+    },
+    {
+      tabs: [
+        { entries: [{ url: "http://example.com#1" }], extData: { "uniq": r() } },
+        { entries: [{ url: "http://example.com#2" }], extData: { "uniq": r() } },
+        { entries: [{ url: "http://example.com#3" }], extData: { "uniq": r() } },
+        { entries: [{ url: "http://example.com#4" }], extData: { "uniq": r() } },
+        { entries: [{ url: "http://example.com#5" }], extData: { "uniq": r() } },
+        { entries: [{ url: "http://example.com#6" }], extData: { "uniq": r() } }
+      ],
+      selected: 4
+    }
+  ] };
+  let numTabs = state.windows[0].tabs.length + state.windows[1].tabs.length;
+
+  let loadCount = 0;
+  gProgressListener.setCallback(function (aBrowser, aNeedRestore, aRestoring, aRestored) {
+    if (++loadCount == numTabs) {
+      // We don't actually care about load order in this test, just that they all
+      // do load.
+      is(loadCount, numTabs, "all tabs were restored");
+      is(aNeedRestore, 0, "there are no tabs left needing restore");
+
+      gProgressListener.unsetCallback();
+      executeSoon(next);
+    }
+  });
+
+  // We also want to catch the 2nd window, so we need to observe domwindowopened
+  Services.ww.registerNotification(function observer(aSubject, aTopic, aData) {
+    if (aTopic == "domwindowopened") {
+      let win = aSubject.QueryInterface(Ci.nsIDOMWindow);
+      win.addEventListener("load", function onLoad() {
+        win.removeEventListener("load", onLoad);
+        Services.ww.unregisterNotification(observer);
+        win.gBrowser.addTabsProgressListener(gProgressListener);
+      });
+    }
+  });
+
+  yield ss.setBrowserState(JSON.stringify(state));
+}