--- a/widget/cocoa/TextInputHandler.h
+++ b/widget/cocoa/TextInputHandler.h
@@ -751,16 +751,21 @@ public:
 public:
   virtual bool OnDestroyWidget(nsChildView* aDestroyingWidget) override;
 
   virtual void OnFocusChangeInGecko(bool aFocus);
 
   void OnSelectionChange(const IMENotification& aIMENotification);
 
   /**
+   * Call [NSTextInputContext handleEvent] for mouse event support of IME
+   */
+  bool OnHandleEvent(NSEvent* aEvent);
+
+  /**
    * SetMarkedText() is a handler of setMarkedText of NSTextInput.
    *
    * @param aAttrString           This mut be an instance of NSAttributedString.
    *                              If the aString parameter to
    *                              [ChildView setMarkedText:setSelectedRange:]
    *                              isn't an instance of NSAttributedString,
    *                              create an NSAttributedString from it and pass
    *                              that instead.

--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -3962,16 +3962,26 @@ IMEInputHandler::OnSelectionChange(const
   mRangeForWritingMode =
     NSMakeRange(aIMENotification.mSelectionChangeData.mOffset,
                 aIMENotification.mSelectionChangeData.Length());
   if (mIMEHasFocus) {
     mSelectedRange = mRangeForWritingMode;
   }
 }
 
+bool
+IMEInputHandler::OnHandleEvent(NSEvent* aEvent)
+{
+  if (!IsFocused()) {
+    return false;
+  }
+  NSTextInputContext* inputContext = [mView inputContext];
+  return [inputContext handleEvent:aEvent];
+}
+
 #pragma mark -
 
 
 /******************************************************************************
  *
  *  TextInputHandlerBase implementation
  *
  ******************************************************************************/

--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -4508,16 +4508,19 @@ NSEvent* gLastDragMouseDownEvent = nil;
 #if USE_CLICK_HOLD_CONTEXTMENU
   // fire off timer to check for click-hold after two seconds. retains |theEvent|
   [self performSelector:@selector(clickHoldCallback:) withObject:theEvent afterDelay:2.0];
 #endif
 
   // in order to send gecko events we'll need a gecko widget
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   NSUInteger modifierFlags = [theEvent modifierFlags];
 
   WidgetMouseEvent geckoEvent(true, eMouseDown, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
 
   NSInteger clickCount = [theEvent clickCount];
@@ -4542,16 +4545,19 @@ NSEvent* gLastDragMouseDownEvent = nil;
 }
 
 - (void)mouseUp:(NSEvent *)theEvent
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   if (!mGeckoChild || mBlockedLastMouseDown)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
 
   WidgetMouseEvent geckoEvent(true, eMouseUp, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   if ([theEvent modifierFlags] & NSControlKeyMask)
     geckoEvent.button = WidgetMouseEvent::eRightButton;
@@ -4671,32 +4677,38 @@ NewCGSRegionFromRegion(const LayoutDevic
 }
 
 - (void)handleMouseMoved:(NSEvent*)theEvent
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseMove, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
 
   mGeckoChild->DispatchInputEvent(&geckoEvent);
 
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
 - (void)mouseDragged:(NSEvent*)theEvent
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   gLastDragView = self;
 
   WidgetMouseEvent geckoEvent(true, eMouseMove, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
 
   mGeckoChild->DispatchInputEvent(&geckoEvent);
@@ -4714,16 +4726,19 @@ NewCGSRegionFromRegion(const LayoutDevic
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
 
   [self maybeRollup:theEvent];
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   // The right mouse went down, fire off a right mouse down event to gecko
   WidgetMouseEvent geckoEvent(true, eMouseDown, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eRightButton;
   geckoEvent.clickCount = [theEvent clickCount];
 
@@ -4738,16 +4753,19 @@ NewCGSRegionFromRegion(const LayoutDevic
 }
 
 - (void)rightMouseUp:(NSEvent *)theEvent
 {
   NS_OBJC_BEGIN_TRY_ABORT_BLOCK;
 
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseUp, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eRightButton;
   geckoEvent.clickCount = [theEvent clickCount];
 
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
@@ -4755,16 +4773,19 @@ NewCGSRegionFromRegion(const LayoutDevic
 
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
 - (void)rightMouseDragged:(NSEvent*)theEvent
 {
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseMove, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eRightButton;
 
   // send event into Gecko by going directly to the
   // the widget.
@@ -4778,46 +4799,55 @@ NewCGSRegionFromRegion(const LayoutDevic
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
 
   if ([self maybeRollup:theEvent] ||
       !ChildViewMouseTracker::WindowAcceptsEvent([self window], theEvent, self))
     return;
 
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseDown, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eMiddleButton;
   geckoEvent.clickCount = [theEvent clickCount];
 
   mGeckoChild->DispatchInputEvent(&geckoEvent);
 
   NS_OBJC_END_TRY_ABORT_BLOCK;
 }
 
 - (void)otherMouseUp:(NSEvent *)theEvent
 {
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseUp, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eMiddleButton;
 
   nsAutoRetainCocoaObject kungFuDeathGrip(self);
   mGeckoChild->DispatchInputEvent(&geckoEvent);
 }
 
 - (void)otherMouseDragged:(NSEvent*)theEvent
 {
   if (!mGeckoChild)
     return;
+  if (mTextInputHandler->OnHandleEvent(theEvent)) {
+    return;
+  }
 
   WidgetMouseEvent geckoEvent(true, eMouseMove, mGeckoChild,
                               WidgetMouseEvent::eReal);
   [self convertCocoaMouseEvent:theEvent toGeckoEvent:&geckoEvent];
   geckoEvent.button = WidgetMouseEvent::eMiddleButton;
 
   // send event into Gecko by going directly to the
   // the widget.