diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_465215.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_465215.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,37 @@
+/* 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 465215 **/
+
+  waitForExplicitFinish();
+
+  let uniqueName = "bug 465215";
+  let uniqueValue1 = "as good as unique: " + Date.now();
+  let uniqueValue2 = "as good as unique: " + Math.random();
+
+  // set a unique value on a new, blank tab
+  let tab1 = gBrowser.addTab();
+  whenBrowserLoaded(tab1.linkedBrowser, function() {
+    ss.setTabValue(tab1, uniqueName, uniqueValue1);
+
+    // duplicate the tab with that value
+    let tab2 = ss.duplicateTab(window, tab1);
+    is(ss.getTabValue(tab2, uniqueName), uniqueValue1, "tab value was duplicated");
+
+    ss.setTabValue(tab2, uniqueName, uniqueValue2);
+    isnot(ss.getTabValue(tab1, uniqueName), uniqueValue2, "tab values aren't sync'd");
+
+    // overwrite the tab with the value which should remove it
+    ss.setTabState(tab1, JSON.stringify({ entries: [] }));
+    whenTabRestored(tab1, function() {
+      is(ss.getTabValue(tab1, uniqueName), "", "tab value was cleared");
+
+      // clean up
+      gBrowser.removeTab(tab2);
+      gBrowser.removeTab(tab1);
+      finish();
+    });
+  });
+}