diff -r 000000000000 -r 6474c204b198 browser/devtools/styleeditor/test/browser_styleeditor_loading.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/styleeditor/test/browser_styleeditor_loading.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,37 @@
+/* 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 TESTCASE_URI = TEST_BASE + "longload.html";
+
+
+function test()
+{
+  waitForExplicitFinish();
+
+  // launch Style Editor right when the tab is created (before load)
+  // this checks that the Style Editor still launches correctly when it is opened
+  // *while* the page is still loading. The Style Editor should not signal that
+  // it is loaded until the accompanying content page is loaded.
+
+  addTabAndCheckOnStyleEditorAdded(function(panel) {
+    content.location = TESTCASE_URI;
+  }, testEditorAdded);
+}
+
+function testEditorAdded(event, editor)
+{
+  let root = gPanelWindow.document.querySelector(".splitview-root");
+  ok(!root.classList.contains("loading"),
+     "style editor root element does not have 'loading' class name anymore");
+
+  let button = gPanelWindow.document.querySelector(".style-editor-newButton");
+  ok(!button.hasAttribute("disabled"),
+     "new style sheet button is enabled");
+
+  button = gPanelWindow.document.querySelector(".style-editor-importButton");
+  ok(!button.hasAttribute("disabled"),
+     "import button is enabled");
+
+  finish();
+}