diff --git a/browser/base/content/test/tabview/browser_tabview_bug580412.js b/browser/base/content/test/tabview/browser_tabview_bug580412.js
new file mode 100644
index 00000000000..45f2b42efde
--- /dev/null
+++ b/browser/base/content/test/tabview/browser_tabview_bug580412.js
@@ -0,0 +1,154 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Tab View bug 580412 test.
+ *
+ * The Initial Developer of the Original Code is
+ * Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2010
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ * Michael Yoshitaka Erlewine <mitcho@mitcho.com>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+function test() {
+  waitForExplicitFinish();
+
+  window.addEventListener("tabviewshown", onTabViewWindowLoaded, false);
+  if (TabView.isVisible())
+    onTabViewWindowLoaded();
+  else
+    TabView.show();
+}
+
+function onTabViewWindowLoaded() {
+  window.removeEventListener("tabviewshown", onTabViewWindowLoaded, false);
+
+  let contentWindow = document.getElementById("tab-view").contentWindow;
+  let [originalTab] = gBrowser.visibleTabs;
+
+  ok(TabView.isVisible(), "Tab View is visible");
+  is(contentWindow.GroupItems.groupItems.length, 1, "There is only one group");
+  let currentActiveGroup = contentWindow.GroupItems.getActiveGroupItem();
+
+//  is(currentActiveGroup.getBounds.bottom(), 40,
+//    "There's currently 40 px between the first group and second group");
+
+  let endGame = function() {
+    let onTabViewHidden = function() {
+      window.removeEventListener("tabviewhidden", onTabViewHidden, false);
+      ok(!TabView.isVisible(), "TabView is shown");
+      finish();
+    };
+    window.addEventListener("tabviewhidden", onTabViewHidden, false);
+
+    ok(TabView.isVisible(), "TabView is shown");
+    
+    gBrowser.selectedTab = originalTab;
+    TabView.hide();
+  }
+  
+  let part1 = function() {
+//    contentWindow.UI.reset();
+    // move down 20 so we're far enough away from the top.
+    checkSnap(currentActiveGroup, 0, 20, contentWindow, function(snapped){
+      ok(!snapped,"Move away from the edge");
+
+      // Just pick it up and drop it.
+      checkSnap(currentActiveGroup, 0, 0, contentWindow, function(snapped){
+        ok(!snapped,"Just pick it up and drop it");
+        
+        checkSnap(currentActiveGroup, 0, 1, contentWindow, function(snapped){
+          ok(snapped,"Drag one pixel: should snap");
+    
+          checkSnap(currentActiveGroup, 0, 5, contentWindow, function(snapped){
+            ok(!snapped,"Moving five pixels: shouldn't snap");
+            endGame();
+          });
+        });
+      });
+    });
+  }
+  
+  part1();
+}
+
+function simulateDragDrop(tabItem, offsetX, offsetY, contentWindow) {
+  // enter drag mode
+  let dataTransfer;
+
+  EventUtils.synthesizeMouse(
+    tabItem.container, 1, 1, { type: "mousedown" }, contentWindow);
+  event = contentWindow.document.createEvent("DragEvents");
+  event.initDragEvent(
+    "dragenter", true, true, contentWindow, 0, 0, 0, 0, 0,
+    false, false, false, false, 1, null, dataTransfer);
+  tabItem.container.dispatchEvent(event);
+
+  // drag over
+  if (offsetX || offsetY) {
+    let Ci = Components.interfaces;
+    let utils = contentWindow.QueryInterface(Ci.nsIInterfaceRequestor).
+                              getInterface(Ci.nsIDOMWindowUtils);
+    let rect = tabItem.getBounds();
+    for (let i = 1; i <= 5; i++) {
+      let left = rect.left + 1 + Math.round(i * offsetX / 5);
+      let top = rect.top + 1 + Math.round(i * offsetY / 5);
+      utils.sendMouseEvent("mousemove", left, top, 0, 1, 0);
+    }
+    event = contentWindow.document.createEvent("DragEvents");
+    event.initDragEvent(
+      "dragover", true, true, contentWindow, 0, 0, 0, 0, 0,
+      false, false, false, false, 0, null, dataTransfer);
+    tabItem.container.dispatchEvent(event);
+  }
+  
+  // drop
+  EventUtils.synthesizeMouse(
+    tabItem.container, 0, 0, { type: "mouseup" }, contentWindow);
+  event = contentWindow.document.createEvent("DragEvents");
+  event.initDragEvent(
+    "drop", true, true, contentWindow, 0, 0, 0, 0, 0,
+    false, false, false, false, 0, null, dataTransfer);
+  tabItem.container.dispatchEvent(event);
+}
+
+function checkSnap(item, offsetX, offsetY, contentWindow, callback) {
+  let firstTop = item.getBounds().top;
+  let firstLeft = item.getBounds().left;
+  let onDrop = function() {
+    let snapped = false;
+    item.container.removeEventListener('drop', onDrop, false);
+    if (item.getBounds().top != firstTop + offsetY)
+      snapped = true;
+    if (item.getBounds().left != firstLeft + offsetX)
+      snapped = true;
+    callback(snapped);
+  };
+  item.container.addEventListener('drop', onDrop, false);
+  simulateDragDrop(item, offsetX, offsetY, contentWindow);
+}