diff -r 000000000000 -r 6474c204b198 browser/components/tabview/test/browser_tabview_bug587503.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/test/browser_tabview_bug587503.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,112 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function test() {
+  waitForExplicitFinish();
+
+  function moveTabOutOfGroup(aTab, aGroup, aCW, aCallback) {
+    let tabPos = aTab.getBounds().center();
+    let groupPos = aGroup.getBounds();
+    let groupPosX = (groupPos.left + groupPos.right) / 2;
+    let groupPosY = groupPos.bottom + 200;
+    let offsetX = Math.round(groupPosX - tabPos.x);
+    let offsetY = Math.round(groupPosY - tabPos.y);
+
+    simulateDragDrop(aTab, offsetX, offsetY, aCW);
+  }
+
+  function moveTabInGroup(aTab, aIndexTo, aGroup, aCW) {
+    let tabTo = aGroup.getChild(aIndexTo);
+    let tabPos = aTab.getBounds().center();
+    let tabToPos = tabTo.getBounds().center();
+    let offsetX = Math.round(tabToPos.x - tabPos.x);
+    let offsetY = Math.round(tabToPos.y - tabPos.y);
+
+    simulateDragDrop(aTab, offsetX, offsetY, aCW);
+  }
+
+  function getTabNumbers(aGroup) {
+    return aGroup.getChildren().map(function (child) {
+      let url = child.tab.linkedBrowser.currentURI.spec;
+      return url.replace("about:blank#", "");
+    }).join(",");
+  }
+
+  function moveTabs(aGroup, aCW) {
+    // Test 1: Move the last tab to the third position.
+    let tab = aGroup.getChild(6);
+    moveTabInGroup(tab, 2, aGroup, aCW);
+    is(getTabNumbers(aGroup), "0,1,6,2,3,4,5", "Validate tab positions in test 1.");
+
+    // Test 2: Move the second tab to the end of the list.
+    tab = aGroup.getChild(1);
+    moveTabInGroup(tab, 6, aGroup, aCW);
+    is(getTabNumbers(aGroup), "0,6,2,3,4,5,1", "Validate tab positions in test 2.");
+
+    // Test 3: Move the fifth tab outside the group.
+    tab = aGroup.getChild(4);
+    moveTabOutOfGroup(tab, aGroup, aCW);
+    is(getTabNumbers(aGroup), "0,6,2,3,5,1", "Validate tab positions in test 3.");
+    is(aCW.GroupItems.groupItems.length, 3, "Validate group count in test 3.");
+
+    // This test is disabled because it is fragile -- see bug 797975
+    if (false) {
+      // Test 4: Move the fifth tab back into the group, on the second row.
+      waitForTransition(tab, function() {
+	moveTabInGroup(tab, 4, aGroup, aCW);
+	is(getTabNumbers(aGroup), "0,6,2,3,4,5,1", "Validate tab positions in test 4.");
+	is(aCW.GroupItems.groupItems.length, 2, "Validate group count in test 4.");
+	closeGroupItem(aGroup, function() { hideTabView(finish) });
+      });
+    } else {
+      closeGroupItem(aGroup, function() { hideTabView(finish) });
+    }
+  }
+
+  function createGroup(win) {
+    registerCleanupFunction(function() win.close());
+    let cw = win.TabView.getContentWindow();
+    let group = createGroupItemWithTabs(win, 400, 430, 100, [
+      "about:blank#0", "about:blank#1", "about:blank#2", "about:blank#3",
+      "about:blank#4", "about:blank#5", "about:blank#6"
+    ]);
+    let groupSize = group.getChildren().length;
+
+    is(cw.GroupItems.groupItems.length, 2, "Validate group count in tab view.");
+    ok(!group.shouldStack(groupSize), "Check that group should not stack.");
+    is(group._columns, 3, "Check the there should be three columns.");
+
+    moveTabs(group, cw);
+  }
+
+  newWindowWithTabView(createGroup);
+}
+
+function simulateDragDrop(aTab, aOffsetX, aOffsetY, aCW) {
+  let target = aTab.container;
+  let rect = target.getBoundingClientRect();
+  let startX = (rect.right - rect.left) / 2;
+  let startY = (rect.bottom - rect.top) / 2;
+  let steps = 2;
+  let incrementX = aOffsetX / steps;
+  let incrementY = aOffsetY / steps;
+
+  EventUtils.synthesizeMouse(
+    target, startX, startY, { type: "mousedown" }, aCW);
+  for (let i = 1; i <= steps; i++) {
+    EventUtils.synthesizeMouse(
+      target, incrementX + startX, incrementY + startY,
+      { type: "mousemove" }, aCW);
+  };
+  EventUtils.synthesizeMouseAtCenter(target, { type: "mouseup" }, aCW);
+}
+
+function waitForTransition(aTab, aCallback) {
+  let groupContainer = aTab.parent.container;
+  groupContainer.addEventListener("transitionend", function onTransitionEnd(aEvent) {
+    if (aEvent.target == groupContainer) {
+      groupContainer.removeEventListener("transitionend", onTransitionEnd);
+      executeSoon(aCallback);
+    }
+  });
+}