diff -r 000000000000 -r 6474c204b198 browser/components/tabview/test/browser_tabview_bug625424.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/test/browser_tabview_bug625424.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  let win;
+  let cw;
+
+  let getGroupItem = function (index) {
+    return cw.GroupItems.groupItems[index];
+  }
+
+  let newWindow = function (test) {
+    newWindowWithTabView(function (tvwin) {
+      registerCleanupFunction(function () {
+        if (!tvwin.closed)
+          tvwin.close();
+      });
+
+      win = tvwin;
+      cw = win.TabView.getContentWindow();
+
+      // setup group items
+      getGroupItem(0).setSize(200, 200, true);
+      createGroupItemWithBlankTabs(win, 200, 200, 300, 1);
+
+      test();
+    });
+  }
+
+  let assertNumberOfTabsInGroupItem = function (groupItem, numTabs) {
+    is(groupItem.getChildren().length, numTabs,
+        'there are ' + numTabs + ' tabs in this groupItem');
+  }
+
+  let testDragOnHiddenGroup = function () {
+    let groupItem = getGroupItem(1);
+
+    hideGroupItem(groupItem, function () {
+      let drag = groupItem.getChild(0).container;
+      let drop = groupItem.$undoContainer[0];
+
+      assertNumberOfTabsInGroupItem(groupItem, 1);
+
+      EventUtils.synthesizeMouseAtCenter(drag, {type: 'mousedown'}, cw);
+      EventUtils.synthesizeMouseAtCenter(drop, {type: 'mousemove'}, cw);
+      EventUtils.synthesizeMouseAtCenter(drop, {type: 'mouseup'}, cw);
+
+      assertNumberOfTabsInGroupItem(groupItem, 1);
+
+      win.close();
+      newWindow(testDragOnVisibleGroup);
+    });
+  }
+
+  let testDragOnVisibleGroup = function () {
+    let groupItem = getGroupItem(0);
+    let drag = getGroupItem(1).getChild(0).container;
+    let drop = groupItem.container;
+
+    assertNumberOfTabsInGroupItem(groupItem, 1);
+
+    EventUtils.synthesizeMouseAtCenter(drag, {type: 'mousedown'}, cw);
+    EventUtils.synthesizeMouseAtCenter(drop, {type: 'mousemove'}, cw);
+    EventUtils.synthesizeMouseAtCenter(drop, {type: 'mouseup'}, cw);
+
+    assertNumberOfTabsInGroupItem(groupItem, 2);
+
+    win.close();
+    finish();
+  }
+
+  waitForExplicitFinish();
+  newWindow(testDragOnHiddenGroup);
+}