diff -r 000000000000 -r 6474c204b198 browser/components/tabview/test/browser_tabview_bug606905.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/test/browser_tabview_bug606905.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,32 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  waitForExplicitFinish();
+
+  let newTabs = []
+  // add enough tabs so the close buttons are hidden and then check the closebuttons attribute
+  do {
+    let newTab = gBrowser.addTab("about:blank", {skipAnimation: true});
+    newTabs.push(newTab);
+  } while (gBrowser.visibleTabs[0].getBoundingClientRect().width > gBrowser.tabContainer.mTabClipWidth)
+
+  // a setTimeout() in addTab is used to trigger adjustTabstrip() so we need a delay here as well.
+  executeSoon(function() {
+    is(gBrowser.tabContainer.getAttribute("closebuttons"), "activetab", "Only show button on selected tab.");
+
+    // move a tab to another group and check the closebuttons attribute
+    TabView._initFrame(function() {
+      TabView.moveTabTo(newTabs[newTabs.length - 1], null);
+      ok(gBrowser.visibleTabs[0].getBoundingClientRect().width > gBrowser.tabContainer.mTabClipWidth, 
+         "Tab width is bigger than tab clip width");
+      is(gBrowser.tabContainer.getAttribute("closebuttons"), "", "Show button on all tabs.")
+
+      // clean up and finish
+      newTabs.forEach(function(tab) {
+        gBrowser.removeTab(tab);
+      });
+      finish();
+    });
+  });
+}