diff -r 000000000000 -r 6474c204b198 browser/devtools/scratchpad/test/browser_scratchpad_tab.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/scratchpad/test/browser_scratchpad_tab.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,77 @@
+/* vim: set ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+/* Bug 660560 */
+
+function test()
+{
+  waitForExplicitFinish();
+
+  gBrowser.selectedTab = gBrowser.addTab();
+  gBrowser.selectedBrowser.addEventListener("load", function onTabLoad() {
+    gBrowser.selectedBrowser.removeEventListener("load", onTabLoad, true);
+
+    ok(window.Scratchpad, "Scratchpad variable exists");
+
+    Services.prefs.setIntPref("devtools.editor.tabsize", 5);
+
+    openScratchpad(runTests);
+  }, true);
+
+  content.location = "data:text/html,Scratchpad test for the Tab key, bug 660560";
+}
+
+function runTests()
+{
+  let sp = gScratchpadWindow.Scratchpad;
+  ok(sp, "Scratchpad object exists in new window");
+
+  ok(sp.editor.hasFocus(), "the editor has focus");
+
+  sp.setText("window.foo;");
+  sp.editor.setCursor({ line: 0, ch: 0 });
+
+  EventUtils.synthesizeKey("VK_TAB", {}, gScratchpadWindow);
+
+  is(sp.getText(), "     window.foo;", "Tab key added 5 spaces");
+
+  is(sp.editor.getCursor().line, 0, "line is correct");
+  is(sp.editor.getCursor().ch, 5, "character is correct");
+
+  sp.editor.setCursor({ line: 0, ch: 6 });
+
+  EventUtils.synthesizeKey("VK_TAB", {}, gScratchpadWindow);
+
+  is(sp.getText(), "     w    indow.foo;",
+     "Tab key added 4 spaces");
+
+  is(sp.editor.getCursor().line, 0, "line is correct");
+  is(sp.editor.getCursor().ch, 10, "character is correct");
+
+  gScratchpadWindow.close();
+
+  Services.prefs.setIntPref("devtools.editor.tabsize", 6);
+  Services.prefs.setBoolPref("devtools.editor.expandtab", false);
+
+  openScratchpad(runTests2);
+}
+
+function runTests2()
+{
+  let sp = gScratchpadWindow.Scratchpad;
+
+  sp.setText("window.foo;");
+  sp.editor.setCursor({ line: 0, ch: 0 });
+
+  EventUtils.synthesizeKey("VK_TAB", {}, gScratchpadWindow);
+
+  is(sp.getText(), "\twindow.foo;", "Tab key added the tab character");
+
+  is(sp.editor.getCursor().line, 0, "line is correct");
+  is(sp.editor.getCursor().ch, 1, "character is correct");
+
+  Services.prefs.clearUserPref("devtools.editor.tabsize");
+  Services.prefs.clearUserPref("devtools.editor.expandtab");
+
+  finish();
+}