diff --git a/docshell/base/moz.build b/docshell/base/moz.build
index f5a398b51912..2fe80c744f23 100644
--- a/docshell/base/moz.build
+++ b/docshell/base/moz.build
@@ -37,6 +37,7 @@ XPIDL_MODULE = 'docshell'
 EXPORTS += [
     'nsDocShellLoadTypes.h',
     'nsILinkHandler.h',
+    'nsIScrollObserver.h',
     'nsIWebShellServices.h',
     'SerializedLoadContext.h',
 ]
diff --git a/docshell/base/nsDocShell.cpp b/docshell/base/nsDocShell.cpp
index 25f6c4e553b9..91e2e37a73a7 100644
--- a/docshell/base/nsDocShell.cpp
+++ b/docshell/base/nsDocShell.cpp
@@ -67,6 +67,7 @@
 #include "nsITimedChannel.h"
 #include "nsIPrivacyTransitionObserver.h"
 #include "nsIReflowObserver.h"
+#include "nsIScrollObserver.h"
 #include "nsIDocShellTreeItem.h"
 #include "nsIChannel.h"
 #include "IHistory.h"
@@ -2857,6 +2858,39 @@ nsDocShell::GetCurrentDocChannel()
     return nullptr;
 }
 
+NS_IMETHODIMP
+nsDocShell::AddWeakScrollObserver(nsIScrollObserver* aObserver)
+{
+    nsWeakPtr weakObs = do_GetWeakReference(aObserver);
+    if (!weakObs) {
+        return NS_ERROR_FAILURE;
+    }
+    return mScrollObservers.AppendElement(weakObs) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsDocShell::RemoveWeakScrollObserver(nsIScrollObserver* aObserver)
+{
+    nsWeakPtr obs = do_GetWeakReference(aObserver);
+    return mScrollObservers.RemoveElement(obs) ? NS_OK : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+nsDocShell::NotifyScrollObservers()
+{
+    nsTObserverArray<nsWeakPtr>::ForwardIterator iter(mScrollObservers);
+    while (iter.HasMore()) {
+        nsWeakPtr ref = iter.GetNext();
+        nsCOMPtr<nsIScrollObserver> obs = do_QueryReferent(ref);
+        if (obs) {
+            obs->ScrollPositionChanged();
+        } else {
+            mScrollObservers.RemoveElement(ref);
+        }
+    }
+    return NS_OK;
+}
+
 //*****************************************************************************
 // nsDocShell::nsIDocShellTreeItem
 //*****************************************************************************   
diff --git a/docshell/base/nsDocShell.h b/docshell/base/nsDocShell.h
index 83ac34f86588..c19177742107 100644
--- a/docshell/base/nsDocShell.h
+++ b/docshell/base/nsDocShell.h
@@ -900,6 +900,7 @@ private:
     nsCOMPtr<nsIPrincipal> mParentCharsetPrincipal;
     nsTObserverArray<nsWeakPtr> mPrivacyObservers;
     nsTObserverArray<nsWeakPtr> mReflowObservers;
+    nsTObserverArray<nsWeakPtr> mScrollObservers;
     nsCString         mOriginalUriString;
 
     // Separate function to do the actual name (i.e. not _top, _self etc.)
diff --git a/docshell/base/nsIDocShell.idl b/docshell/base/nsIDocShell.idl
index 1a9cf2bccf9c..2d2cb57df9a1 100644
--- a/docshell/base/nsIDocShell.idl
+++ b/docshell/base/nsIDocShell.idl
@@ -41,6 +41,7 @@ interface nsIWebBrowserPrint;
 interface nsIVariant;
 interface nsIPrivacyTransitionObserver;
 interface nsIReflowObserver;
+interface nsIScrollObserver;
 
 typedef unsigned long nsLoadFlags;
 
@@ -667,6 +668,24 @@ interface nsIDocShell : nsIDocShellTreeItem
                                         in DOMHighResTimeStamp start,
                                         in DOMHighResTimeStamp end);
 
+  /**
+   * Add an observer to the list of parties to be notified when scroll position
+   * of some elements is changed.
+   */
+  [noscript] void addWeakScrollObserver(in nsIScrollObserver obs);
+
+  /**
+   * Add an observer to the list of parties to be notified when scroll position
+   * of some elements is changed.
+   */
+  [noscript] void removeWeakScrollObserver(in nsIScrollObserver obs);
+
+  /**
+   * Notify all attached observers that the scroll position of some element
+   * has changed.
+   */
+  [noscript] void notifyScrollObservers();
+
   /**
    * Returns true if this docshell corresponds to an <iframe mozbrowser>.
    * (<iframe mozapp mozbrowser> is not considered a browser.)
diff --git a/docshell/base/nsIScrollObserver.h b/docshell/base/nsIScrollObserver.h
new file mode 100644
index 000000000000..ba756296ed88
--- /dev/null
+++ b/docshell/base/nsIScrollObserver.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; 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/. */
+
+#ifndef nsIScrollObserver_h___
+#define nsIScrollObserver_h___
+
+#include "nsISupports.h"
+
+#define NS_ISCROLLOBSERVER_IID \
+  { 0x7c1a8b63, 0xe322, 0x4827, \
+    { 0xa4, 0xb1, 0x3b, 0x6e, 0x59, 0x03, 0x47, 0x7e } }
+
+class nsIScrollObserver : public nsISupports
+{
+public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ISCROLLOBSERVER_IID)
+
+  /**
+   * Called when the scroll position of some element has changed.
+   */
+  virtual void ScrollPositionChanged() = 0;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsIScrollObserver, NS_ISCROLLOBSERVER_IID)
+
+#endif /* nsIScrollObserver_h___ */
diff --git a/dom/events/nsIMEStateManager.cpp b/dom/events/nsIMEStateManager.cpp
index 5393be127be8..4110c6c94944 100644
--- a/dom/events/nsIMEStateManager.cpp
+++ b/dom/events/nsIMEStateManager.cpp
@@ -35,6 +35,10 @@
 #include "TextComposition.h"
 #include "mozilla/Preferences.h"
 #include "nsAsyncDOMEvent.h"
+#include "nsIDocShell.h"
+#include "nsIReflowObserver.h"
+#include "nsIScrollObserver.h"
+#include "nsWeakReference.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
@@ -46,7 +50,10 @@ using namespace mozilla::widget;
 // sTextStateObserver is null if there is no focused editor
 
 class nsTextStateManager MOZ_FINAL : public nsISelectionListener,
-                                     public nsStubMutationObserver
+                                     public nsStubMutationObserver,
+                                     public nsIReflowObserver,
+                                     public nsIScrollObserver,
+                                     public nsSupportsWeakReference
 {
 public:
   nsTextStateManager()
@@ -61,6 +68,10 @@ public:
   NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
   NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTEWILLCHANGE
   NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTECHANGED
+  NS_DECL_NSIREFLOWOBSERVER
+
+  // nsIScrollObserver
+  virtual void ScrollPositionChanged() MOZ_OVERRIDE;
 
   void     Init(nsIWidget* aWidget,
                 nsPresContext* aPresContext,
@@ -82,6 +93,7 @@ private:
   void NotifyContentAdded(nsINode* aContainer, int32_t aStart, int32_t aEnd);
   void ObserveEditableNode();
 
+  nsCOMPtr<nsIDocShell>          mDocShell;
   nsIMEUpdatePreference mUpdatePreference;
   uint32_t mPreAttrChangeLength;
 };
@@ -752,6 +764,8 @@ nsTextStateManager::Init(nsIWidget* aWidget,
     return;
   }
 
+  mDocShell = aPresContext->GetDocShell();
+
   ObserveEditableNode();
 }
 
@@ -774,6 +788,13 @@ nsTextStateManager::ObserveEditableNode()
     // add text change observer
     mRootContent->AddMutationObserver(this);
   }
+
+  if (mUpdatePreference.WantPositionChanged() && mDocShell) {
+    // Add scroll position listener and reflow observer to detect position and
+    // size changes
+    mDocShell->AddWeakScrollObserver(this);
+    mDocShell->AddWeakReflowObserver(this);
+  }
 }
 
 void
@@ -800,8 +821,13 @@ nsTextStateManager::Destroy(void)
   if (mUpdatePreference.WantTextChange() && mRootContent) {
     mRootContent->RemoveMutationObserver(this);
   }
+  if (mUpdatePreference.WantPositionChanged() && mDocShell) {
+    mDocShell->RemoveWeakScrollObserver(this);
+    mDocShell->RemoveWeakReflowObserver(this);
+  }
   mRootContent = nullptr;
   mEditableNode = nullptr;
+  mDocShell = nullptr;
   mUpdatePreference.mWantUpdates = nsIMEUpdatePreference::NOTIFY_NOTHING;
 }
 
@@ -833,9 +859,12 @@ nsTextStateManager::IsEditorHandlingEventForComposition() const
   return composition->IsEditorHandlingEvent();
 }
 
-NS_IMPL_ISUPPORTS2(nsTextStateManager,
+NS_IMPL_ISUPPORTS5(nsTextStateManager,
                    nsIMutationObserver,
-                   nsISelectionListener)
+                   nsISelectionListener,
+                   nsIReflowObserver,
+                   nsIScrollObserver,
+                   nsISupportsWeakReference)
 
 // Helper class, used for selection change notification
 class SelectionChangeEvent : public nsRunnable {
@@ -917,6 +946,54 @@ private:
   bool mCausedByComposition;
 };
 
+class PositionChangeEvent MOZ_FINAL : public nsRunnable
+{
+public:
+  PositionChangeEvent(nsTextStateManager* aDispatcher)
+    : mDispatcher(aDispatcher) {
+    MOZ_ASSERT(mDispatcher);
+  }
+
+  NS_IMETHOD Run() {
+    if (mDispatcher->mWidget) {
+      mDispatcher->mWidget->NotifyIME(
+        IMENotification(NOTIFY_IME_OF_POSITION_CHANGE));
+    }
+    return NS_OK;
+  }
+
+private:
+  nsRefPtr<nsTextStateManager> mDispatcher;
+};
+
+void
+nsTextStateManager::ScrollPositionChanged()
+{
+  if (mWidget) {
+    nsContentUtils::AddScriptRunner(new PositionChangeEvent(this));
+  }
+}
+
+NS_IMETHODIMP
+nsTextStateManager::Reflow(DOMHighResTimeStamp aStart,
+                           DOMHighResTimeStamp aEnd)
+{
+  if (mWidget) {
+    nsContentUtils::AddScriptRunner(new PositionChangeEvent(this));
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsTextStateManager::ReflowInterruptible(DOMHighResTimeStamp aStart,
+                                        DOMHighResTimeStamp aEnd)
+{
+  if (mWidget) {
+    nsContentUtils::AddScriptRunner(new PositionChangeEvent(this));
+  }
+  return NS_OK;
+}
+
 void
 nsTextStateManager::CharacterDataChanged(nsIDocument* aDocument,
                                          nsIContent* aContent,
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 7f011c494780..5a31048656c5 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -2085,6 +2085,8 @@ ScrollFrameHelper::ScrollToImpl(nsPoint aPt, const nsRect& aRange, nsIAtom* aOri
   for (uint32_t i = 0; i < mListeners.Length(); i++) {
     mListeners[i]->ScrollPositionDidChange(pt.x, pt.y);
   }
+
+  presContext->GetDocShell()->NotifyScrollObservers();
 }
 
 static void
diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index 6d698e328aba..f9ff356b13fa 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -226,6 +226,7 @@ struct nsIMEUpdatePreference {
     NOTIFY_NOTHING                       = 0,
     NOTIFY_SELECTION_CHANGE              = 1 << 0,
     NOTIFY_TEXT_CHANGE                   = 1 << 1,
+    NOTIFY_POSITION_CHANGE               = 1 << 2,
     // Following values indicate when widget needs or doesn't need notification.
     NOTIFY_CHANGES_CAUSED_BY_COMPOSITION = 1 << 6,
     // NOTE: NOTIFY_DURING_DEACTIVE isn't supported in environments where two
@@ -264,6 +265,11 @@ struct nsIMEUpdatePreference {
     return !!(mWantUpdates & NOTIFY_TEXT_CHANGE);
   }
 
+  bool WantPositionChanged() const
+  {
+    return !!(mWantUpdates & NOTIFY_POSITION_CHANGE);
+  }
+
   bool WantChanges() const
   {
     return WantSelectionChange() || WantTextChange();
@@ -492,6 +498,8 @@ enum IMEMessage MOZ_ENUM_TYPE(int8_t)
   NOTIFY_IME_OF_TEXT_CHANGE,
   // Composition string has been updated
   NOTIFY_IME_OF_COMPOSITION_UPDATE,
+  // Position or size of focused element may be changed.
+  NOTIFY_IME_OF_POSITION_CHANGE,
   // Request to commit current composition to IME
   // (some platforms may not support)
   REQUEST_TO_COMMIT_COMPOSITION,