--- a/dom/base/test/chrome/window_nsITextInputProcessor.xul
+++ b/dom/base/test/chrome/window_nsITextInputProcessor.xul
@@ -152,17 +152,19 @@ function runBeginInputTransactionMethodT
   ok(TIP2.beginInputTransaction(otherWindow, simpleCallback),
      description + "TIP2.beginInputTransaction(otherWindow) should succeed because there is composition synthesized by TIP1 but it's in other window");
   ok(TIP2.beginInputTransactionForTests(otherWindow),
      description + "TIP2.beginInputTransactionForTests(otherWindow) should succeed because there is composition synthesized by TIP1 but it's in other window");
 
   // Let's confirm that the composing string is NOT committed by above tests.
   TIP1.commitComposition();
   is(input.value, composingStr,
-     description + "TIP1.commitString() without specifying commit string should be committed with the last composing string");
+     description + "TIP1.commitString() without specifying commit string should commit current composition with the last composing string");
+  ok(!TIP1.hasComposition,
+     description + "TIP1.commitString() without specifying commit string should've end composition");
 
   ok(TIP1.beginInputTransaction(window, simpleCallback),
      description + "TIP1.beginInputTransaction() should succeed because there is no composition #2");
   ok(TIP1.beginInputTransactionForTests(window),
      description + "TIP1.beginInputTransactionForTests() should succeed because there is no composition #2");
   ok(TIP2.beginInputTransactionForTests(window),
      description + "TIP2.beginInputTransactionForTests() should succeed because the composition was already committed #2");
 

--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -1928,16 +1928,32 @@ void
 nsBaseWidget::EnsureTextEventDispatcher()
 {
   if (mTextEventDispatcher) {
     return;
   }
   mTextEventDispatcher = new TextEventDispatcher(this);
 }
 
+nsIWidget::NativeIMEContext
+nsBaseWidget::GetNativeIMEContext()
+{
+  if (mTextEventDispatcher && mTextEventDispatcher->GetPseudoIMEContext()) {
+    // If we already have a TextEventDispatcher and it's working with
+    // a TextInputProcessor, we need to return pseudo IME context since
+    // TextCompositionArray::IndexOf(nsIWidget*) should return a composition
+    // on the pseudo IME context in such case.
+    NativeIMEContext pseudoIMEContext;
+    pseudoIMEContext.InitWithRawNativeIMEContext(
+                       mTextEventDispatcher->GetPseudoIMEContext());
+    return pseudoIMEContext;
+  }
+  return NativeIMEContext(this);
+}
+
 nsIWidget::TextEventDispatcher*
 nsBaseWidget::GetTextEventDispatcher()
 {
   EnsureTextEventDispatcher();
   return mTextEventDispatcher;
 }
 
 void*
@@ -2436,22 +2452,16 @@ nsBaseWidget::DefaultFillScrollCapture(D
   aSnapshotDrawTarget->FillRect(
     gfx::Rect(0, 0, dtSize.width, dtSize.height),
     gfx::ColorPattern(gfx::Color::FromABGR(kScrollCaptureFillColor)),
     gfx::DrawOptions(1.f, gfx::CompositionOp::OP_SOURCE));
   aSnapshotDrawTarget->Flush();
 }
 #endif
 
-nsIWidget::NativeIMEContext
-nsIWidget::GetNativeIMEContext()
-{
-  return NativeIMEContext(this);
-}
-
 const IMENotificationRequests&
 nsIWidget::IMENotificationRequestsRef()
 {
   TextEventDispatcher* dispatcher = GetTextEventDispatcher();
   return dispatcher->IMENotificationRequestsRef();
 }
 
 nsresult

--- a/widget/nsBaseWidget.h
+++ b/widget/nsBaseWidget.h
@@ -293,16 +293,17 @@ public:
   CreateChild(const LayoutDeviceIntRect& aRect,
               nsWidgetInitData* aInitData = nullptr,
               bool aForceUseIWidgetParent = false) override;
   virtual void            AttachViewToTopLevel(bool aUseAttachedEvents) override;
   virtual nsIWidgetListener* GetAttachedWidgetListener() override;
   virtual void               SetAttachedWidgetListener(nsIWidgetListener* aListener) override;
   virtual nsIWidgetListener* GetPreviouslyAttachedWidgetListener() override;
   virtual void               SetPreviouslyAttachedWidgetListener(nsIWidgetListener* aListener) override;
+  virtual NativeIMEContext GetNativeIMEContext() override;
   TextEventDispatcher* GetTextEventDispatcher() final;
   virtual TextEventDispatcherListener*
     GetNativeTextEventDispatcherListener() override;
   virtual void ZoomToRect(const uint32_t& aPresShellId,
                           const FrameMetrics::ViewID& aViewId,
                           const CSSRect& aRect,
                           const uint32_t& aFlags) override;
   // Dispatch an event that must be first be routed through APZ.

--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -1846,17 +1846,17 @@ public:
      */
     virtual InputContext GetInputContext() = 0;
 
     /**
      * Get native IME context.  This is different from GetNativeData() with
      * NS_RAW_NATIVE_IME_CONTEXT, the result is unique even if in a remote
      * process.
      */
-    virtual NativeIMEContext GetNativeIMEContext();
+    virtual NativeIMEContext GetNativeIMEContext() = 0;
 
     /*
      * Given a WidgetKeyboardEvent, this method synthesizes a corresponding
      * native (OS-level) event for it. This method allows tests to simulate
      * keystrokes that trigger native key bindings (which require a native
      * event).
      */
     virtual MOZ_MUST_USE nsresult