new file mode 100644
--- /dev/null
+++ b/dom/webidl/CaretStateChangedEvent.webidl
@@ -0,0 +1,32 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+enum CaretChangedReason {
+  "visibilitychange",
+  "updateposition",
+  "longpressonemptycontent",
+  "taponcaret",
+  "presscaret",
+  "releasecaret"
+};
+
+dictionary CaretStateChangedEventInit : EventInit {
+  boolean collapsed = true;
+  DOMRectReadOnly? boundingClientRect = null;
+  CaretChangedReason reason = "visibilitychange";
+  boolean caretVisible = false;
+  boolean selectionVisible = false;
+};
+
+[Constructor(DOMString type, optional CaretStateChangedEventInit eventInit),
+ ChromeOnly]
+interface CaretStateChangedEvent : Event {
+  readonly attribute boolean collapsed;
+  readonly attribute DOMRectReadOnly? boundingClientRect;
+  readonly attribute CaretChangedReason reason;
+  readonly attribute boolean caretVisible;
+  readonly attribute boolean selectionVisible;
+};

--- a/dom/webidl/moz.build
+++ b/dom/webidl/moz.build
@@ -722,16 +722,17 @@ GENERATED_EVENTS_WEBIDL_FILES = [
     'AutocompleteErrorEvent.webidl',
     'BlobEvent.webidl',
     'CallEvent.webidl',
     'CallGroupErrorEvent.webidl',
     'CameraClosedEvent.webidl',
     'CameraConfigurationEvent.webidl',
     'CameraFacesDetectedEvent.webidl',
     'CameraStateChangeEvent.webidl',
+    'CaretStateChangedEvent.webidl',
     'CFStateChangeEvent.webidl',
     'CloseEvent.webidl',
     'CSSFontFaceLoadEvent.webidl',
     'DataErrorEvent.webidl',
     'DataStoreChangeEvent.webidl',
     'DeviceLightEvent.webidl',
     'DeviceOrientationEvent.webidl',
     'DeviceProximityEvent.webidl',

--- a/layout/base/AccessibleCaretManager.cpp
+++ b/layout/base/AccessibleCaretManager.cpp
@@ -861,9 +861,80 @@ AccessibleCaretManager::LaunchCaretTimeo
 void
 AccessibleCaretManager::CancelCaretTimeoutTimer()
 {
   if (mCaretTimeoutTimer) {
     mCaretTimeoutTimer->Cancel();
   }
 }
 
+void
+AccessibleCaretManager::DispatchCaretStateChangedEvent(CaretChangedReason aReason) const
+{
+  MOZ_ASSERT(nsContentUtils::IsSafeToRunScript());
+  // Holding PresShell to prevent AccessibleCaretManager to be destroyed.
+  nsCOMPtr<nsIPresShell> presShell = mPresShell;
+  // XXX: Do we need to flush layout?
+  presShell->FlushPendingNotifications(Flush_Layout);
+  if (presShell->IsDestroying()) {
+    return;
+  }
+
+  Selection* sel = GetSelection();
+  if (!sel) {
+    return;
+  }
+
+  nsIDocument* doc = mPresShell->GetDocument();
+  MOZ_ASSERT(doc);
+
+  CaretStateChangedEventInit init;
+  init.mBubbles = true;
+
+  const nsRange* range = sel->GetAnchorFocusRange();
+  nsINode* commonAncestorNode = nullptr;
+  if (range) {
+    commonAncestorNode = range->GetCommonAncestor();
+  }
+
+  if (!commonAncestorNode) {
+    commonAncestorNode = sel->GetFrameSelection()->GetAncestorLimiter();
+  }
+
+  nsRefPtr<DOMRect> domRect = new DOMRect(ToSupports(doc));
+  nsRect rect = nsContentUtils::GetSelectionBoundingRect(sel);
+
+  nsIFrame* commonAncestorFrame = nullptr;
+  nsIFrame* rootFrame = mPresShell->GetRootFrame();
+
+  if (commonAncestorNode && commonAncestorNode->IsContent()) {
+    commonAncestorFrame = commonAncestorNode->AsContent()->GetPrimaryFrame();
+  }
+
+  if (commonAncestorFrame && rootFrame) {
+    nsLayoutUtils::TransformRect(rootFrame, commonAncestorFrame, rect);
+    nsRect clampedRect = nsLayoutUtils::ClampRectToScrollFrames(commonAncestorFrame,
+                                                                rect);
+    nsLayoutUtils::TransformRect(commonAncestorFrame, rootFrame, clampedRect);
+    domRect->SetLayoutRect(clampedRect);
+    init.mSelectionVisible = !clampedRect.IsEmpty();
+    init.mBoundingClientRect = domRect;
+  } else {
+    domRect->SetLayoutRect(rect);
+    init.mSelectionVisible = true;
+  }
+
+  init.mBoundingClientRect = domRect;
+  init.mReason = aReason;
+  init.mCollapsed = sel->IsCollapsed();
+  init.mCaretVisible = mFirstCaret->IsLogicallyVisible() ||
+                       mSecondCaret->IsLogicallyVisible();
+
+  nsRefPtr<CaretStateChangedEvent> event =
+    CaretStateChangedEvent::Constructor(doc, NS_LITERAL_STRING("mozcaretstatechanged"), init);
+
+  event->SetTrusted(true);
+  event->GetInternalNSEvent()->mFlags.mOnlyChromeDispatch = true;
+  bool ret;
+  doc->DispatchEvent(event, &ret);
+}
+
 } // namespace mozilla

--- a/layout/base/AccessibleCaretManager.h
+++ b/layout/base/AccessibleCaretManager.h
@@ -8,16 +8,17 @@
 #define AccessibleCaretManager_h
 
 #include "nsCOMPtr.h"
 #include "nsCoord.h"
 #include "nsIFrame.h"
 #include "nsISelectionListener.h"
 #include "nsRefPtr.h"
 #include "nsWeakReference.h"
+#include "mozilla/dom/CaretStateChangedEvent.h"
 #include "mozilla/EventForwards.h"
 #include "mozilla/UniquePtr.h"
 #include "mozilla/WeakPtr.h"
 
 class nsFrameSelection;
 class nsIContent;
 class nsIPresShell;
 struct nsPoint;
@@ -127,16 +128,20 @@ protected:
   nsresult DragCaretInternal(const nsPoint& aPoint);
   nsPoint AdjustDragBoundary(const nsPoint& aPoint) const;
   void ClearMaintainedSelection() const;
 
   dom::Selection* GetSelection() const;
   already_AddRefed<nsFrameSelection> GetFrameSelection() const;
   nsIContent* GetFocusedContent() const;
 
+  // This function will call FlushPendingNotifications. So caller must ensure
+  // everything exists after calling this method.
+  void DispatchCaretStateChangedEvent(dom::CaretChangedReason aReason) const;
+
   // If we're dragging the first caret, we do not want to drag it over the
   // previous character of the second caret. Same as the second caret. So we
   // check if content offset exceeds the previous/next character of second/first
   // caret base the active caret.
   bool CompareRangeWithContentOffset(nsIFrame::ContentOffsets& aOffsets);
 
   // Timeout in milliseconds to hide the AccessibleCaret under cursor mode while
   // no one touches it.