diff -r 000000000000 -r 6474c204b198 browser/base/content/tabbrowser.css
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/tabbrowser.css	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,65 @@
+/* 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/. */
+
+.tabbrowser-tabbox {
+  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-tabbox");
+}
+
+.tabbrowser-arrowscrollbox {
+  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-arrowscrollbox");
+}
+
+.tab-close-button {
+  -moz-binding: url("chrome://browser/content/tabbrowser.xml#tabbrowser-close-tab-button");
+}
+
+.tab-close-button[pinned],
+.tabbrowser-tabs[closebuttons="activetab"] > * > * > * > .tab-close-button:not([selected="true"]) {
+  display: none;
+}
+
+.tab-label[pinned] {
+  width: 0;
+  margin-left: 0 !important;
+  margin-right: 0 !important;
+  padding-left: 0 !important;
+  padding-right: 0 !important;
+}
+
+.tab-stack {
+  vertical-align: top; /* for pinned tabs */
+}
+
+tabpanels {
+  background-color: transparent;
+}
+
+.tab-drop-indicator {
+  position: relative;
+  z-index: 2;
+}
+
+.tab-icon-image:not([src]):not([pinned]),
+.tab-throbber:not([busy]),
+.tab-throbber[busy] + .tab-icon-image {
+  display: none;
+}
+
+.closing-tabs-spacer {
+  pointer-events: none;
+}
+
+.tabbrowser-tabs:not(:hover) > .tabbrowser-arrowscrollbox > .closing-tabs-spacer {
+  transition: width .15s ease-out;
+}
+
+/**
+ * Optimization for tabs that are restored lazily. We can save a good amount of
+ * memory that to-be-restored tabs would otherwise consume simply by setting
+ * their browsers to 'display: none' as that will prevent them from having to
+ * create a presentation and the like.
+ */
+browser[pending] {
+  display: none;
+}