diff -r 000000000000 -r 6474c204b198 browser/devtools/styleeditor/test/browser_styleeditor_private_perwindowpb.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/styleeditor/test/browser_styleeditor_private_perwindowpb.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,57 @@
+/* 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/. */
+
+// This test makes sure that the style editor does not store any
+// content CSS files in the permanent cache when opened from PB mode.
+
+let gUI;
+
+function test() {
+  waitForExplicitFinish();
+  let windowsToClose = [];
+  let testURI = 'http://' + TEST_HOST + '/browser/browser/devtools/styleeditor/test/test_private.html';
+
+  function checkCache() {
+    checkDiskCacheFor(TEST_HOST, function() {
+      gUI = null;
+      finish();
+    });
+  }
+
+  function doTest(aWindow) {
+    aWindow.gBrowser.selectedBrowser.addEventListener("load", function onLoad() {
+      aWindow.gBrowser.selectedBrowser.removeEventListener("load", onLoad, true);
+      cache.clear();
+      openStyleEditorInWindow(aWindow, function(panel) {
+        gUI = panel.UI;
+        gUI.on("editor-added", onEditorAdded);
+      });
+    }, true);
+
+    aWindow.gBrowser.selectedBrowser.loadURI(testURI);
+  }
+
+  function onEditorAdded(aEvent, aEditor) {
+    aEditor.getSourceEditor().then(checkCache);
+  }
+
+  function testOnWindow(options, callback) {
+    let win = OpenBrowserWindow(options);
+    win.addEventListener("load", function onLoad() {
+      win.removeEventListener("load", onLoad, false);
+      windowsToClose.push(win);
+      executeSoon(function() callback(win));
+    }, false);
+  };
+
+  registerCleanupFunction(function() {
+    windowsToClose.forEach(function(win) {
+      win.close();
+    });
+  });
+
+  testOnWindow({private: true}, function(win) {
+    doTest(win);
+  });
+}