diff -r 000000000000 -r 6474c204b198 browser/devtools/scratchpad/test/browser_scratchpad_browser_last_window_closing.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/scratchpad/test/browser_scratchpad_browser_last_window_closing.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,79 @@
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const BUTTON_POSITION_CANCEL     = 1;
+const BUTTON_POSITION_DONT_SAVE  = 2;
+
+
+function test()
+{
+  waitForExplicitFinish();
+
+  // Observer must be attached *before* Scratchpad is opened.
+  CloseObserver.init();
+
+  gBrowser.selectedTab = gBrowser.addTab();
+  gBrowser.selectedBrowser.addEventListener("load", function onTabLoad() {
+    gBrowser.selectedBrowser.removeEventListener("load", onTabLoad, true);
+    openScratchpad(runTests);
+  }, true);
+
+  content.location = "data:text/html;charset=utf8,<p>test browser last window closing</p>";
+}
+
+
+
+function runTests({ Scratchpad })
+{
+  let browser = Services.wm.getEnumerator("navigator:browser").getNext();
+  let oldPrompt = Services.prompt;
+  let button;
+
+  Services.prompt = {
+    confirmEx: () => button
+  };
+
+
+  Scratchpad.dirty = true;
+
+  // Test canceling close.
+  button = BUTTON_POSITION_CANCEL;
+  CloseObserver.expectedValue = true;
+  browser.BrowserTryToCloseWindow();
+
+  // Test accepting close.
+  button = BUTTON_POSITION_DONT_SAVE;
+  CloseObserver.expectedValue = false;
+  browser.BrowserTryToCloseWindow();
+
+  // Test closing without prompt needed.
+  Scratchpad.dirty = false;
+  browser.BrowserTryToCloseWindow();
+
+  Services.prompt = oldPrompt;
+  CloseObserver.uninit();
+  finish();
+}
+
+
+let CloseObserver = {
+  expectedValue: null,
+  init: function()
+  {
+    Services.obs.addObserver(this, "browser-lastwindow-close-requested", false);
+  },
+
+  observe: function(aSubject)
+  {
+    aSubject.QueryInterface(Ci.nsISupportsPRBool);
+    let message = this.expectedValue ? "close" : "stay open";
+    ok(this.expectedValue === aSubject.data, "Expected browser to " + message);
+    aSubject.data = true;
+  },
+
+  uninit: function()
+  {
+    Services.obs.removeObserver(this, "browser-lastwindow-close-requested", false);
+  },
+};