diff -r 000000000000 -r 6474c204b198 browser/components/tabview/test/browser_tabview_bug634672.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/test/browser_tabview_bug634672.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,52 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  let cw;
+  let win;
+
+  waitForExplicitFinish();
+
+  newWindowWithTabView(function (tvwin) {
+    win = tvwin;
+    cw = win.TabView.getContentWindow();
+
+    registerCleanupFunction(function () {
+      if (win && !win.closed)
+        win.close();
+    });
+
+    // fill the group item with some tabs
+    for (let i = 0; i < 5; i++)
+      win.gBrowser.loadOneTab("about:blank");
+
+    let groupItem = cw.GroupItems.groupItems[0];
+    groupItem.setSize(400, 400, true);
+    let range = new cw.Range(1, 400);
+
+    // determine the groupItem's largest possible stacked size
+    while (range.extent > 1) {
+      let pivot = Math.floor(range.extent / 2);
+      groupItem.setSize(range.min + pivot, range.min + pivot, true);
+
+      if (groupItem.isStacked())
+        range.min += pivot;
+      else
+        range.max -= pivot;
+    }
+
+    // stack the group
+    groupItem.setSize(range.min, range.min, true);
+    ok(groupItem.isStacked(), "groupItem is stacked");
+
+    // one step back to un-stack the groupItem
+    groupItem.setSize(range.max, range.max, true);
+    ok(!groupItem.isStacked(), "groupItem is no longer stacked");
+
+    // check that close buttons are visible
+    let tabItem = groupItem.getChild(0);
+    isnot(tabItem.$close.css("display"), "none", "close button is visible");
+
+    finish();
+  });
+}