diff -r 000000000000 -r 6474c204b198 browser/devtools/debugger/debugger.css
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/debugger/debugger.css	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,50 @@
+/* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
+/* 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/. */
+
+/* Side pane views */
+
+#sources-pane > tabpanels > tabpanel,
+#instruments-pane > tabpanels > tabpanel {
+  -moz-box-orient: vertical;
+}
+
+/* Toolbar controls */
+
+.devtools-toolbarbutton:not([label]) > .toolbarbutton-text {
+  display: none;
+}
+
+/* Horizontal vs. vertical layout */
+
+#body[layout=vertical] #debugger-widgets {
+  -moz-box-orient: vertical;
+}
+
+#body[layout=vertical] #sources-pane {
+  -moz-box-flex: 1;
+}
+
+#body[layout=vertical] #instruments-pane {
+  -moz-box-flex: 2;
+}
+
+#body[layout=vertical] #instruments-pane-toggle {
+  display: none;
+}
+
+#body[layout=vertical] #sources-and-editor-splitter,
+#body[layout=vertical] #editor-and-instruments-splitter {
+  display: none;
+}
+
+#body[layout=horizontal] #vertical-layout-splitter,
+#body[layout=horizontal] #vertical-layout-panes-container {
+  display: none;
+}
+
+#body[layout=vertical] #stackframes {
+  visibility: hidden;
+}