--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -4889,18 +4889,36 @@ PRBool nsWindow::ProcessMessage(UINT msg
 
     case WM_MBUTTONUP:
       result = DispatchMouseEvent(NS_MOUSE_BUTTON_UP, wParam, lParam, PR_FALSE,
                                   nsMouseEvent::eMiddleButton, MOUSE_INPUT_SOURCE());
       DispatchPendingEvents();
       break;
 
     case WM_MBUTTONDBLCLK:
-      result = DispatchMouseEvent(NS_MOUSE_BUTTON_DOWN, wParam, lParam, PR_FALSE,
+      result = DispatchMouseEvent(NS_MOUSE_DOUBLECLICK, wParam, lParam, PR_FALSE,
+                                  nsMouseEvent::eMiddleButton, MOUSE_INPUT_SOURCE());
+      break;
+
+    case WM_NCMBUTTONDOWN:
+      result = DispatchMouseEvent(NS_MOUSE_BUTTON_DOWN, 0, lParamToClient(lParam), PR_FALSE,
                                   nsMouseEvent::eMiddleButton, MOUSE_INPUT_SOURCE());
+      DispatchPendingEvents();
+      break;
+
+    case WM_NCMBUTTONUP:
+      result = DispatchMouseEvent(NS_MOUSE_BUTTON_UP, 0, lParamToClient(lParam), PR_FALSE,
+                                  nsMouseEvent::eMiddleButton, MOUSE_INPUT_SOURCE());
+      DispatchPendingEvents();
+      break;
+
+    case WM_NCMBUTTONDBLCLK:
+      result = DispatchMouseEvent(NS_MOUSE_DOUBLECLICK, 0, lParamToClient(lParam), PR_FALSE,
+                                  nsMouseEvent::eMiddleButton, MOUSE_INPUT_SOURCE());
+      DispatchPendingEvents();
       break;
 
     case WM_RBUTTONDOWN:
     {
       result = DispatchMouseEvent(NS_MOUSE_BUTTON_DOWN, wParam, lParam, PR_FALSE,
                                   nsMouseEvent::eRightButton, MOUSE_INPUT_SOURCE());
       DispatchPendingEvents();
     }