diff -r 000000000000 -r 6474c204b198 browser/base/content/test/general/browser_lastAccessedTab.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/test/general/browser_lastAccessedTab.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  let originalTab = gBrowser.selectedTab;
+  isnot(originalTab.lastAccessed, 0, "selectedTab has been selected");
+  ok(originalTab.lastAccessed <= Date.now(), "selectedTab has a valid timestamp");
+
+  let newTab = gBrowser.addTab("about:blank", {skipAnimation: true});
+  is(newTab.lastAccessed, 0, "newTab hasn't been selected so far");
+
+  gBrowser.selectedTab = newTab;
+
+  isnot(newTab.lastAccessed, 0, "newTab has been selected");
+  ok(newTab.lastAccessed <= Date.now(), "newTab has a valid timestamp");
+
+  isnot(originalTab.lastAccessed, 0, "originalTab has been selected");
+  ok(originalTab.lastAccessed <= Date.now(), "originalTab has a valid timestamp");
+
+  ok(originalTab.lastAccessed <= newTab.lastAccessed,
+     "originalTab's timestamp must be lower than newTab's");
+
+  gBrowser.removeTab(newTab);
+}