diff -r 000000000000 -r 6474c204b198 browser/components/tabview/test/browser_tabview_dragdrop.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/test/browser_tabview_dragdrop.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,89 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  waitForExplicitFinish();
+  showTabView(onTabViewShown);
+}
+
+function onTabViewShown() {
+  ok(TabView.isVisible(), "Tab View is visible");
+
+  let contentWindow = TabView.getContentWindow();
+  let [originalTab] = gBrowser.visibleTabs;
+
+  let createGroupItem = function (left, top, width, height) {
+    let box = new contentWindow.Rect(left, top, width, height);
+    let groupItem = new contentWindow.GroupItem([], {bounds: box, immediately: true});
+
+    contentWindow.UI.setActive(groupItem);
+    gBrowser.loadOneTab("about:blank", {inBackground: true});
+
+    return groupItem;
+  };
+
+  // create group one and two
+  let groupOne = createGroupItem(20, 20, 300, 300);
+  let groupTwo = createGroupItem(20, 400, 300, 300);
+
+  waitForFocus(function () {
+    addTest(contentWindow, groupOne.id, groupTwo.id, originalTab);
+  });
+}
+
+function addTest(contentWindow, groupOneId, groupTwoId, originalTab) {
+  let groupOne = contentWindow.GroupItems.groupItem(groupOneId);
+  let groupTwo = contentWindow.GroupItems.groupItem(groupTwoId);
+  let groupOneTabItemCount = groupOne.getChildren().length;
+  let groupTwoTabItemCount = groupTwo.getChildren().length;
+  is(groupOneTabItemCount, 1, "GroupItem one has one tab");
+  is(groupTwoTabItemCount, 1, "GroupItem two has one tab as well");
+
+  let tabItem = groupOne.getChild(0);
+  ok(tabItem, "The tab item exists");
+
+  // calculate the offsets
+  let groupTwoRectCenter = groupTwo.getBounds().center();
+  let tabItemRectCenter = tabItem.getBounds().center();
+  let offsetX =
+    Math.round(groupTwoRectCenter.x - tabItemRectCenter.x);
+  let offsetY =
+    Math.round(groupTwoRectCenter.y - tabItemRectCenter.y);
+
+  function endGame() {
+    groupTwo.removeSubscriber("childAdded", endGame);
+
+    is(groupOne.getChildren().length, --groupOneTabItemCount,
+       "The number of children in group one is decreased by 1");
+    is(groupTwo.getChildren().length, ++groupTwoTabItemCount,
+       "The number of children in group two is increased by 1");
+
+    closeGroupItem(groupOne, function () {
+      closeGroupItem(groupTwo, function () hideTabView(finish));
+    });
+  }
+
+  groupTwo.addSubscriber("childAdded", endGame);
+  simulateDragDrop(tabItem.container, offsetX, offsetY, contentWindow);
+}
+
+function simulateDragDrop(element, offsetX, offsetY, contentWindow) {
+  let rect = element.getBoundingClientRect();
+  let startX = (rect.right - rect.left)/2;
+  let startY = (rect.bottom - rect.top)/2;
+  let incrementX = offsetX / 2;
+  let incrementY = offsetY / 2;
+
+  EventUtils.synthesizeMouse(
+    element, startX, startY, { type: "mousedown" });
+  
+  for (let i = 1; i <= 2; i++) {
+    EventUtils.synthesizeMouse(
+      element, (startX + incrementX * i), (startY + incrementY * i), 
+      { type: "mousemove" });
+  }
+
+  EventUtils.synthesizeMouse(
+    element, (startX + incrementX * 2), (startY + incrementY * 2), 
+    { type: "mouseup" });
+}