diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_465223.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_465223.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,48 @@
+/* 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/. */
+
+function test() {
+  /** Test for Bug 465223 **/
+
+  // test setup
+  waitForExplicitFinish();
+
+  let uniqueKey1 = "bug 465223.1";
+  let uniqueKey2 = "bug 465223.2";
+  let uniqueValue1 = "unik" + Date.now();
+  let uniqueValue2 = "pi != " + Math.random();
+
+  // open a window and set a value on it
+  let newWin = openDialog(location, "_blank", "chrome,all,dialog=no");
+  newWin.addEventListener("load", function(aEvent) {
+    newWin.removeEventListener("load", arguments.callee, false);
+
+    ss.setWindowValue(newWin, uniqueKey1, uniqueValue1);
+
+    let newState = { windows: [{ tabs:[{ entries: [] }], extData: {} }] };
+    newState.windows[0].extData[uniqueKey2] = uniqueValue2;
+    ss.setWindowState(newWin, JSON.stringify(newState), false);
+
+    is(newWin.gBrowser.tabs.length, 2,
+       "original tab wasn't overwritten");
+    is(ss.getWindowValue(newWin, uniqueKey1), uniqueValue1,
+       "window value wasn't overwritten when the tabs weren't");
+    is(ss.getWindowValue(newWin, uniqueKey2), uniqueValue2,
+       "new window value was correctly added");
+
+    newState.windows[0].extData[uniqueKey2] = uniqueValue1;
+    ss.setWindowState(newWin, JSON.stringify(newState), true);
+
+    is(newWin.gBrowser.tabs.length, 1,
+       "original tabs were overwritten");
+    is(ss.getWindowValue(newWin, uniqueKey1), "",
+       "window value was cleared");
+    is(ss.getWindowValue(newWin, uniqueKey2), uniqueValue1,
+       "window value was correctly overwritten");
+
+    // clean up
+    newWin.close();
+    finish();
+  }, false);
+}