diff --git a/dom/events/IMEContentObserver.cpp b/dom/events/IMEContentObserver.cpp
index ec5d2f3b197..ef8dd49b017 100644
--- a/dom/events/IMEContentObserver.cpp
+++ b/dom/events/IMEContentObserver.cpp
@@ -852,6 +852,35 @@ IMEContentObserver::PostSelectionChangeNotification(
   mIsSelectionChangeEventPending = true;
 }
 
+bool
+IMEContentObserver::UpdateSelectionCache()
+{
+  MOZ_ASSERT(IsSafeToNotifyIME());
+
+  if (!mUpdatePreference.WantSelectionChange()) {
+    return false;
+  }
+
+  mSelectionData.Clear();
+
+  // XXX Cannot we cache some information for reducing the cost to compute
+  //     selection offset and writing mode?
+  WidgetQueryContentEvent selection(true, NS_QUERY_SELECTED_TEXT, mWidget);
+  ContentEventHandler handler(GetPresContext());
+  handler.OnQuerySelectedText(&selection);
+  if (NS_WARN_IF(!selection.mSucceeded)) {
+    return false;
+  }
+
+  mSelectionData.mOffset = selection.mReply.mOffset;
+  *mSelectionData.mString = selection.mReply.mString;
+  mSelectionData.SetWritingMode(selection.GetWritingMode());
+  mSelectionData.mReversed = selection.mReply.mReversed;
+  mSelectionData.mCausedByComposition = false;
+  mSelectionData.mCausedBySelectionEvent = false;
+  return mSelectionData.IsValid();
+}
+
 void
 IMEContentObserver::PostPositionChangeNotification()
 {
@@ -1060,13 +1089,7 @@ IMEContentObserver::SelectionChangeEvent::Run()
     return NS_OK;
   }
 
-  // XXX Cannot we cache some information for reducing the cost to compute
-  //     selection offset and writing mode?
-  WidgetQueryContentEvent selection(true, NS_QUERY_SELECTED_TEXT,
-                                    mIMEContentObserver->mWidget);
-  ContentEventHandler handler(mIMEContentObserver->GetPresContext());
-  handler.OnQuerySelectedText(&selection);
-  if (NS_WARN_IF(!selection.mSucceeded)) {
+  if (NS_WARN_IF(!mIMEContentObserver->UpdateSelectionCache())) {
     return NS_OK;
   }
 
@@ -1076,15 +1099,8 @@ IMEContentObserver::SelectionChangeEvent::Run()
   }
 
   IMENotification notification(NOTIFY_IME_OF_SELECTION_CHANGE);
-  notification.mSelectionChangeData.mOffset = selection.mReply.mOffset;
-  *notification.mSelectionChangeData.mString = selection.mReply.mString;
-  notification.mSelectionChangeData.SetWritingMode(
-                                      selection.GetWritingMode());
-  notification.mSelectionChangeData.mReversed = selection.mReply.mReversed;
-  notification.mSelectionChangeData.mCausedByComposition =
-    mCausedByComposition;
-  notification.mSelectionChangeData.mCausedBySelectionEvent =
-    mCausedBySelectionEvent;
+  notification.SetData(mIMEContentObserver->mSelectionData,
+                       mCausedByComposition, mCausedBySelectionEvent);
   IMEStateManager::NotifyIME(notification, mIMEContentObserver->mWidget);
   return NS_OK;
 }
@@ -1106,7 +1122,7 @@ IMEContentObserver::TextChangeEvent::Run()
   }
 
   IMENotification notification(NOTIFY_IME_OF_TEXT_CHANGE);
-  notification.mTextChangeData = mTextChangeData;
+  notification.SetData(mTextChangeData);
   IMEStateManager::NotifyIME(notification, mIMEContentObserver->mWidget);
   return NS_OK;
 }
diff --git a/dom/events/IMEContentObserver.h b/dom/events/IMEContentObserver.h
index 77e09f8408a..b22c6d7e88a 100644
--- a/dom/events/IMEContentObserver.h
+++ b/dom/events/IMEContentObserver.h
@@ -40,6 +40,7 @@ class IMEContentObserver final : public nsISelectionListener
                                , public nsIEditorObserver
 {
 public:
+  typedef widget::IMENotification::SelectionChangeData SelectionChangeData;
   typedef widget::IMENotification::TextChangeData TextChangeData;
   typedef widget::IMENotification::TextChangeDataBase TextChangeDataBase;
 
@@ -167,6 +168,15 @@ private:
     mTextChangeData.Clear();
   }
 
+  /**
+   * UpdateSelectionCache() updates mSelectionData with the latest selection.
+   * This should be called only when IsSafeToNotifyIME() returns true.
+   *
+   * Note that this does nothing if mUpdatePreference.WantSelectionChange()
+   * returns false.
+   */
+  bool UpdateSelectionCache();
+
   nsCOMPtr<nsIWidget> mWidget;
   nsCOMPtr<nsISelection> mSelection;
   nsCOMPtr<nsIContent> mRootContent;
@@ -230,6 +240,11 @@ private:
 
   TextChangeData mTextChangeData;
 
+  // mSelectionData is the last selection data which was notified.  This is
+  // modified by UpdateSelectionCache().  Note that mCausedBy* are always
+  // false.  Do NOT refer them.
+  SelectionChangeData mSelectionData;
+
   EventStateManager* mESM;
 
   nsIMEUpdatePreference mUpdatePreference;
diff --git a/widget/IMEData.h b/widget/IMEData.h
index efa798c2687..c0b0ba84127 100644
--- a/widget/IMEData.h
+++ b/widget/IMEData.h
@@ -757,6 +757,27 @@ struct IMENotification final
     MouseButtonEventData mMouseButtonEventData;
   };
 
+  void SetData(const SelectionChangeDataBase& aSelectionChangeData)
+  {
+    MOZ_RELEASE_ASSERT(mMessage == NOTIFY_IME_OF_SELECTION_CHANGE);
+    mSelectionChangeData.Assign(aSelectionChangeData);
+  }
+  void SetData(const SelectionChangeDataBase& aSelectionChangeData,
+               bool aCausedByComposition,
+               bool aCausedBySelectionEvent)
+  {
+    MOZ_RELEASE_ASSERT(mMessage == NOTIFY_IME_OF_SELECTION_CHANGE);
+    mSelectionChangeData.Assign(aSelectionChangeData);
+    mSelectionChangeData.mCausedByComposition = aCausedByComposition;
+    mSelectionChangeData.mCausedBySelectionEvent = aCausedBySelectionEvent;
+  }
+
+  void SetData(const TextChangeDataBase& aTextChangeData)
+  {
+    MOZ_RELEASE_ASSERT(mMessage == NOTIFY_IME_OF_TEXT_CHANGE);
+    mTextChangeData = aTextChangeData;
+  }
+
   bool IsCausedByComposition() const
   {
     switch (mMessage) {