diff -r 000000000000 -r 6474c204b198 browser/components/sessionstore/test/browser_461634.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/sessionstore/test/browser_461634.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,75 @@
+/* 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 461634 **/
+
+  waitForExplicitFinish();
+
+  const REMEMBER = Date.now(), FORGET = Math.random();
+  let test_state = { windows: [{ "tabs": [{ "entries": [] }], _closedTabs: [
+    { state: { entries: [{ url: "http://www.example.net/" }] }, title: FORGET },
+    { state: { entries: [{ url: "http://www.example.net/" }] }, title: REMEMBER },
+    { state: { entries: [{ url: "http://www.example.net/" }] }, title: FORGET },
+    { state: { entries: [{ url: "http://www.example.net/" }] }, title: REMEMBER },
+  ] }] };
+  let remember_count = 2;
+
+  function countByTitle(aClosedTabList, aTitle)
+    aClosedTabList.filter(function(aData) aData.title == aTitle).length;
+
+  function testForError(aFunction) {
+    try {
+      aFunction();
+      return false;
+    }
+    catch (ex) {
+      return ex.name == "NS_ERROR_ILLEGAL_VALUE";
+    }
+  }
+
+  // open a window and add the above closed tab list
+  let newWin = openDialog(location, "", "chrome,all,dialog=no");
+  newWin.addEventListener("load", function(aEvent) {
+    newWin.removeEventListener("load", arguments.callee, false);
+
+    gPrefService.setIntPref("browser.sessionstore.max_tabs_undo",
+                            test_state.windows[0]._closedTabs.length);
+    ss.setWindowState(newWin, JSON.stringify(test_state), true);
+
+    let closedTabs = JSON.parse(ss.getClosedTabData(newWin));
+    is(closedTabs.length, test_state.windows[0]._closedTabs.length,
+       "Closed tab list has the expected length");
+    is(countByTitle(closedTabs, FORGET),
+       test_state.windows[0]._closedTabs.length - remember_count,
+       "The correct amout of tabs are to be forgotten");
+    is(countByTitle(closedTabs, REMEMBER), remember_count,
+       "Everything is set up.");
+
+    // all of the following calls with illegal arguments should throw NS_ERROR_ILLEGAL_VALUE
+    ok(testForError(function() ss.forgetClosedTab({}, 0)),
+       "Invalid window for forgetClosedTab throws");
+    ok(testForError(function() ss.forgetClosedTab(newWin, -1)),
+       "Invalid tab for forgetClosedTab throws");
+    ok(testForError(function() ss.forgetClosedTab(newWin, test_state.windows[0]._closedTabs.length + 1)),
+       "Invalid tab for forgetClosedTab throws");
+
+    // Remove third tab, then first tab
+    ss.forgetClosedTab(newWin, 2);
+    ss.forgetClosedTab(newWin, null);
+
+    closedTabs = JSON.parse(ss.getClosedTabData(newWin));
+    is(closedTabs.length, remember_count,
+       "The correct amout of tabs was removed");
+    is(countByTitle(closedTabs, FORGET), 0,
+       "All tabs specifically forgotten were indeed removed");
+    is(countByTitle(closedTabs, REMEMBER), remember_count,
+       "... and tabs not specifically forgetten weren't.");
+
+    // clean up
+    newWin.close();
+    gPrefService.clearUserPref("browser.sessionstore.max_tabs_undo");
+    finish();
+  }, false);
+}