--- a/dom/events/IMEStateManager.cpp
+++ b/dom/events/IMEStateManager.cpp
@@ -193,38 +193,43 @@ IMEStateManager::Shutdown()
   delete sTextCompositions;
   sTextCompositions = nullptr;
 }
 
 // static
 void
 IMEStateManager::OnTabParentDestroying(TabParent* aTabParent)
 {
+  if (sFocusedIMETabParent == aTabParent) {
+    NotifyIMEOfBlurForChildProcess();
+  }
+
   if (sActiveTabParent != aTabParent) {
     return;
   }
+
   MOZ_LOG(sISMLog, LogLevel::Info,
     ("OnTabParentDestroying(aTabParent=0x%p), "
      "The active TabParent is being destroyed", aTabParent));
 
   // The active remote process might have crashed.
   sActiveTabParent = nullptr;
 
-  // TODO: Need to cancel composition without TextComposition and make
-  //       disable IME.
+  // XXX: Need to disable IME?
 }
 
 // static
 void
 IMEStateManager::WidgetDestroyed(nsIWidget* aWidget)
 {
   if (sWidget == aWidget) {
     sWidget = nullptr;
   }
   if (sFocusedIMEWidget == aWidget) {
+    NotifyIMEOfBlurForChildProcess();
     sFocusedIMEWidget = nullptr;
   }
   if (sActiveInputContextWidget == aWidget) {
     sActiveInputContextWidget = nullptr;
   }
 }
 
 // static
@@ -244,16 +249,37 @@ IMEStateManager::StopIMEStateManagement(
   sPresContext = nullptr;
   sContent = nullptr;
   sActiveTabParent = nullptr;
   DestroyIMEContentObserver();
 }
 
 // static
 void
+IMEStateManager::NotifyIMEOfBlurForChildProcess()
+{
+  MOZ_LOG(sISMLog, LogLevel::Debug,
+    ("NotifyIMEOfBlurForChildProcess(), sFocusedIMETabParent=0x%p, "
+     "sFocusedIMEWidget=0x%p",
+     sFocusedIMETabParent.get(), sFocusedIMEWidget));
+
+  if (!sFocusedIMETabParent) {
+    MOZ_ASSERT(!sFocusedIMEWidget);
+    return;
+  }
+
+  MOZ_ASSERT(sFocusedIMEWidget);
+  NotifyIME(NOTIFY_IME_OF_BLUR, sFocusedIMEWidget, sFocusedIMETabParent);
+
+  MOZ_ASSERT(!sFocusedIMETabParent);
+  MOZ_ASSERT(!sFocusedIMEWidget);
+}
+
+// static
+void
 IMEStateManager::MaybeStartOffsetUpdatedInChild(nsIWidget* aWidget,
                                                 uint32_t aStartOffset)
 {
   if (NS_WARN_IF(!sTextCompositions)) {
     MOZ_LOG(sISMLog, LogLevel::Warning,
       ("MaybeStartOffsetUpdatedInChild(aWidget=0x%p, aStartOffset=%u), "
        "called when there is no composition", aWidget, aStartOffset));
     return;
@@ -484,23 +510,29 @@ IMEStateManager::OnChangeFocusInternal(n
   } else {
     // If there is no active IMEContentObserver, it means that focused content
     // may be in another process.
 
     // If focus is moving from current focused remote process to different
     // process while the process has IME focus too, we need to notify IME of
     // blur here because it may be too late the blur notification to reach
     // this process especially when closing active window.
-    if (sFocusedIMETabParent &&
+    // However, don't send blur if we're being deactivated and IME wants to
+    // keep composition during deactive because notifying blur will commit
+    // or cancel composition.
+    if (sFocusedIMETabParent && sFocusedIMEWidget &&
+        (aPresContext ||
+         !sFocusedIMEWidget->IMENotificationRequestsRef().
+           WantDuringDeactive()) &&
         !IsSameProcess(sFocusedIMETabParent, newTabParent)) {
       MOZ_LOG(sISMLog, LogLevel::Info,
         ("  OnChangeFocusInternal(), notifying IME of blur of previous focused "
          "remote process because it may be too late actual notification to "
          "reach this process"));
-      NotifyIME(NOTIFY_IME_OF_BLUR, sFocusedIMEWidget, sFocusedIMETabParent);
+      NotifyIMEOfBlurForChildProcess();
     }
   }
 
   if (!aPresContext) {
     MOZ_LOG(sISMLog, LogLevel::Debug,
       ("  OnChangeFocusInternal(), "
        "no nsPresContext is being activated"));
     return NS_OK;

--- a/dom/events/IMEStateManager.h
+++ b/dom/events/IMEStateManager.h
@@ -269,16 +269,22 @@ protected:
                               const InputContextAction& aAction);
   static IMEState GetNewIMEState(nsPresContext* aPresContext,
                                  nsIContent* aContent);
 
   static void EnsureTextCompositionArray();
   static void CreateIMEContentObserver(EditorBase* aEditorBase);
   static void DestroyIMEContentObserver();
 
+  /**
+   * NotifyIMEOfBlurForChildProcess() tries to send blur notification when
+   * a remote process has IME focus.  Otherwise, do nothing.
+   */
+  static void NotifyIMEOfBlurForChildProcess();
+
   static bool IsEditable(nsINode* node);
 
   static bool IsIMEObserverNeeded(const IMEState& aState);
 
   static nsIContent* GetRootContent(nsPresContext* aPresContext);
 
   /**
    * CanHandleWith() returns false if aPresContext is nullptr or it's destroyed.