--- a/widget/windows/TSFTextStore.cpp
+++ b/widget/windows/TSFTextStore.cpp
@@ -1849,16 +1849,22 @@ TSFTextStore::MaybeFlushPendingNotificat
     MOZ_LOG(sTextStoreLog, LogLevel::Debug,
            ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
             "mContentForTSF is cleared", this));
   }
 
   // When there is no cached content, we can sync actual contents and TSF/TIP
   // expecting contents.
   if (!mContentForTSF.IsInitialized()) {
+    if (mPendingTextChangeData.IsValid()) {
+      MOZ_LOG(sTextStoreLog, LogLevel::Info,
+             ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
+              "calling TSFTextStore::NotifyTSFOfTextChange()...", this));
+      NotifyTSFOfTextChange();
+    }
     if (mPendingSelectionChangeData.IsValid()) {
       MOZ_LOG(sTextStoreLog, LogLevel::Info,
              ("TSF: 0x%p   TSFTextStore::MaybeFlushPendingNotifications(), "
               "calling TSFTextStore::NotifyTSFOfSelectionChange()...", this));
       NotifyTSFOfSelectionChange();
     }
   }
 
@@ -4577,18 +4583,17 @@ TSFTextStore::GetIMEUpdatePreference()
     }
   }
   return nsIMEUpdatePreference();
 }
 
 nsresult
 TSFTextStore::OnTextChangeInternal(const IMENotification& aIMENotification)
 {
-  const IMENotification::TextChangeDataBase& textChangeData =
-    aIMENotification.mTextChangeData;
+  const TextChangeDataBase& textChangeData = aIMENotification.mTextChangeData;
 
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
          ("TSF: 0x%p   TSFTextStore::OnTextChangeInternal(aIMENotification={ "
           "mMessage=0x%08X, mTextChangeData={ mStartOffset=%lu, "
           "mRemovedEndOffset=%lu, mAddedEndOffset=%lu, "
           "mCausedOnlyByComposition=%s, "
           "mIncludingChangesDuringComposition=%s, "
           "mIncludingChangesWithoutComposition=%s }), "
@@ -4607,96 +4612,87 @@ TSFTextStore::OnTextChangeInternal(const
           GetBoolName(mComposition.IsComposing())));
 
   if (mDestroyed) {
     // If this instance is already destroyed, we shouldn't notify TSF of any
     // changes.
     return NS_OK;
   }
 
-  if (textChangeData.mCausedOnlyByComposition) {
-    // Ignore text change notifications caused only by composition since it's
-    // already been handled internally.
-    return NS_OK;
-  }
-
-  if (mComposition.IsComposing() &&
-      !textChangeData.mIncludingChangesDuringComposition) {
-    // Ignore text changes when they don't include changes caused not by
-    // composition at the latest composition because changes before current
-    // composition start shouldn't cause forcibly committing composition.
-    // In the future, we should notify TSF of such delayed text changes
-    // after current composition is active (In such case,
-    // mIncludingChangesWithoutComposition is true).
-    return NS_OK;
-  }
-
   mDeferNotifyingTSF = false;
 
-  if (IsReadLocked()) {
-    // XXX If text change occurs during the document is locked, it must be
-    //     modified by Javascript.  In such case, we should notify merged
-    //     text changes after it's unlocked.
-    return NS_OK;
-  }
-
-  mSelection.MarkDirty();
-
+  // Different from selection change, we don't modify anything with text
+  // change data.  Therefore, if neither TSF not TIP wants text change
+  // notifications, we don't need to store the changes.
   if (!mSink || !(mSinkMask & TS_AS_TEXT_CHANGE)) {
     return NS_OK;
   }
 
-  if (aIMENotification.mTextChangeData.IsInInt32Range()) {
-    TS_TEXTCHANGE textChange;
-    textChange.acpStart = static_cast<LONG>(textChangeData.mStartOffset);
-    textChange.acpOldEnd = static_cast<LONG>(textChangeData.mRemovedEndOffset);
-    textChange.acpNewEnd = static_cast<LONG>(textChangeData.mAddedEndOffset);
-    NotifyTSFOfTextChange(textChange);
-  } else {
-    MOZ_LOG(sTextStoreLog, LogLevel::Error,
-           ("TSF: 0x%p   TSFTextStore::NotifyTSFOfTextChange() FAILED due to "
-            "offset is too big for calling "
-            "ITextStoreACPSink::OnTextChange()...",
-            this));
-  }
+  // Merge any text change data even if it's caused by composition.
+  mPendingTextChangeData.MergeWith(textChangeData);
 
   MaybeFlushPendingNotifications();
 
   return NS_OK;
 }
 
 void
-TSFTextStore::NotifyTSFOfTextChange(const TS_TEXTCHANGE& aTextChange)
+TSFTextStore::NotifyTSFOfTextChange()
 {
   MOZ_ASSERT(!mDestroyed);
-
-  // XXX We need to cache the text change ranges and notify TSF of that
-  //     the document is unlocked.
-  if (NS_WARN_IF(IsReadLocked())) {
+  MOZ_ASSERT(!IsReadLocked());
+  MOZ_ASSERT(!mComposition.IsComposing());
+  MOZ_ASSERT(mPendingTextChangeData.IsValid());
+
+  // If the text changes are caused only by composition, we don't need to
+  // notify TSF of the text changes.
+  if (mPendingTextChangeData.mCausedOnlyByComposition) {
+    mPendingTextChangeData.Clear();
     return;
   }
 
-  // Some TIPs are confused by text change notification during composition.
-  // Especially, some of them stop working for composition in our process.
-  // For preventing it, let's commit the composition.
-  if (mComposition.IsComposing()) {
-    MOZ_LOG(sTextStoreLog, LogLevel::Info,
-           ("TSF: 0x%p   TSFTextStore::NotifyTSFOfTextChange(), "
-            "committing the composition for avoiding making TIP confused...",
+  // First, forget cached selection.
+  mSelection.MarkDirty();
+
+  // For making it safer, we should check if there is a valid sink to receive
+  // text change notification.
+  if (NS_WARN_IF(!mSink) || NS_WARN_IF(!(mSinkMask & TS_AS_TEXT_CHANGE))) {
+    MOZ_LOG(sTextStoreLog, LogLevel::Error,
+           ("TSF: 0x%p   TSFTextStore::NotifyTSFOfTextChange() FAILED due to "
+            "mSink is not ready to call ITextStoreACPSink::OnTextChange()...",
             this));
-    CommitCompositionInternal(false);
+    mPendingTextChangeData.Clear();
     return;
   }
 
+  if (NS_WARN_IF(!mPendingTextChangeData.IsInInt32Range())) {
+    MOZ_LOG(sTextStoreLog, LogLevel::Error,
+           ("TSF: 0x%p   TSFTextStore::NotifyTSFOfTextChange() FAILED due to "
+            "offset is too big for calling "
+            "ITextStoreACPSink::OnTextChange()...",
+            this));
+    mPendingTextChangeData.Clear();
+    return;
+   }
+
+  TS_TEXTCHANGE textChange;
+  textChange.acpStart =
+    static_cast<LONG>(mPendingTextChangeData.mStartOffset);
+  textChange.acpOldEnd =
+    static_cast<LONG>(mPendingTextChangeData.mRemovedEndOffset);
+  textChange.acpNewEnd =
+    static_cast<LONG>(mPendingTextChangeData.mAddedEndOffset);
+  mPendingTextChangeData.Clear();
+
   MOZ_LOG(sTextStoreLog, LogLevel::Info,
          ("TSF: 0x%p   TSFTextStore::NotifyTSFOfTextChange(), calling "
           "ITextStoreACPSink::OnTextChange(0, { acpStart=%ld, acpOldEnd=%ld, "
-          "acpNewEnd=%ld })...", this, aTextChange.acpStart,
-          aTextChange.acpOldEnd, aTextChange.acpNewEnd));
-  mSink->OnTextChange(0, &aTextChange);
+          "acpNewEnd=%ld })...", this, textChange.acpStart,
+          textChange.acpOldEnd, textChange.acpNewEnd));
+  mSink->OnTextChange(0, &textChange);
 }
 
 nsresult
 TSFTextStore::OnSelectionChangeInternal(const IMENotification& aIMENotification)
 {
   const SelectionChangeDataBase& selectionChangeData =
     aIMENotification.mSelectionChangeData;
   MOZ_LOG(sTextStoreLog, LogLevel::Debug,
@@ -4723,16 +4719,19 @@ TSFTextStore::OnSelectionChangeInternal(
     // changes.
     return NS_OK;
   }
 
   mDeferNotifyingTSF = false;
 
   // Assign the new selection change data to the pending selection change data
   // because only the latest selection data is necessary.
+  // Note that this is necessary to update mSelection.  Therefore, even if
+  // neither TSF nor TIP wants selection change notifications, we need to
+  // store the selection information.
   mPendingSelectionChangeData.Assign(selectionChangeData);
 
   // Flush remaining pending notifications here if it's possible.
   MaybeFlushPendingNotifications();
 
   return NS_OK;
 }
 

--- a/widget/windows/TSFTextStore.h
+++ b/widget/windows/TSFTextStore.h
@@ -51,16 +51,18 @@ struct MSGResult;
 
 class TSFTextStore final : public ITextStoreACP
                          , public ITfContextOwnerCompositionSink
                          , public ITfMouseTrackerACP
 {
 private:
   typedef IMENotification::SelectionChangeDataBase SelectionChangeDataBase;
   typedef IMENotification::SelectionChangeData SelectionChangeData;
+  typedef IMENotification::TextChangeDataBase TextChangeDataBase;
+  typedef IMENotification::TextChangeData TextChangeData;
 
 public: /*IUnknown*/
   STDMETHODIMP          QueryInterface(REFIID, void**);
 
   NS_INLINE_DECL_IUNKNOWN_REFCOUNTING(TSFTextStore)
 
 public: /*ITextStoreACP*/
   STDMETHODIMP AdviseSink(REFIID, IUnknown*, DWORD);
@@ -316,17 +318,22 @@ protected:
   nsresult OnLayoutChangeInternal();
   nsresult OnUpdateCompositionInternal();
 
   // mPendingSelectionChangeData stores selection change data until notifying
   // TSF of selection change.  If two or more selection changes occur, this
   // stores the latest selection change data because only it is necessary.
   SelectionChangeData mPendingSelectionChangeData;
 
-  void     NotifyTSFOfTextChange(const TS_TEXTCHANGE& aTextChange);
+  // mPendingTextChangeData stores one or more text change data until notifying
+  // TSF of text change.  If two or more text changes occur, this merges
+  // every text change data.
+  TextChangeData mPendingTextChangeData;
+
+  void     NotifyTSFOfTextChange();
   void     NotifyTSFOfSelectionChange();
   bool     NotifyTSFOfLayoutChange();
   void     NotifyTSFOfLayoutChangeAgain();
 
   HRESULT  HandleRequestAttrs(DWORD aFlags,
                               ULONG aFilterCount,
                               const TS_ATTRID* aFilterAttrs);
   void     SetInputScope(const nsString& aHTMLInputType,