diff --git a/dom/plugins/PluginInstanceParent.cpp b/dom/plugins/PluginInstanceParent.cpp
index 5790b5eda609..c9ffc6378b01 100644
--- a/dom/plugins/PluginInstanceParent.cpp
+++ b/dom/plugins/PluginInstanceParent.cpp
@@ -903,11 +903,8 @@ PluginInstanceParent::PluginWindowHookProc(HWND hWnd,
 
     switch (message) {
         case WM_SETFOCUS:
-        // Widget may be calling us back from AnswerPluginGotFocus(), make
-        // sure we don't end up sending this back over. If we're not in
-        // SendMessage, this is coming from the dom / focus manager.
-        if ((::InSendMessageEx(NULL) & (ISMEX_SEND|ISMEX_REPLIED)) != ISMEX_SEND)
-            self->CallSetPluginFocus();
+        // Let the child plugin window know it should take focus.
+        self->CallSetPluginFocus();
         break;
 
         case WM_CLOSE:
diff --git a/widget/src/windows/nsWindow.cpp b/widget/src/windows/nsWindow.cpp
index 7101bbba7e68..3b50099e9798 100644
--- a/widget/src/windows/nsWindow.cpp
+++ b/widget/src/windows/nsWindow.cpp
@@ -3655,12 +3655,20 @@ nsWindow::IsAsyncResponseEvent(UINT aMsg, LRESULT& aResult)
   return false;
 }
 
-// static
 void
-nsWindow::IPCWindowProcHandler(HWND& hWnd, UINT& msg, WPARAM& wParam, LPARAM& lParam)
+nsWindow::IPCWindowProcHandler(UINT& msg, WPARAM& wParam, LPARAM& lParam)
 {
   NS_ASSERTION(!mozilla::ipc::SyncChannel::IsPumpingMessages(),
                "Failed to prevent a nonqueued message from running!");
+
+  // Windowed plugins receiving focus triggering WM_ACTIVATE app messages.
+  if (mWindowType == eWindowType_plugin && msg == WM_SETFOCUS &&
+      ::GetPropW(mWnd, L"PluginInstanceParentProperty")) {
+      ::ReplyMessage(0);
+      return;
+  }
+
+  // Modal UI being displayed in windowless plugins.
   if (mozilla::ipc::RPCChannel::IsSpinLoopActive() &&
       (::InSendMessageEx(NULL)&(ISMEX_REPLIED|ISMEX_SEND)) == ISMEX_SEND) {
     LRESULT res;
@@ -3695,8 +3703,12 @@ nsWindow::IPCWindowProcHandler(HWND& hWnd, UINT& msg, WPARAM& wParam, LPARAM& lP
 // The WndProc procedure for all nsWindows in this toolkit
 LRESULT CALLBACK nsWindow::WindowProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {
+  // Get the window which caused the event and ask it to process the message
+  nsWindow *someWindow = GetNSWindowPtr(hWnd);
+
 #ifdef MOZ_IPC
-  IPCWindowProcHandler(hWnd, msg, wParam, lParam);
+  if (someWindow)
+    someWindow->IPCWindowProcHandler(msg, wParam, lParam);
 #endif
 
   // create this here so that we store the last rolled up popup until after
@@ -3707,9 +3719,6 @@ LRESULT CALLBACK nsWindow::WindowProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM
   if ( DealWithPopups(hWnd, msg, wParam, lParam, &popupHandlingResult) )
     return popupHandlingResult;
 
-  // Get the window which caused the event and ask it to process the message
-  nsWindow *someWindow = GetNSWindowPtr(hWnd);
-
   // XXX This fixes 50208 and we are leaving 51174 open to further investigate
   // why we are hitting this assert
   if (nsnull == someWindow) {
diff --git a/widget/src/windows/nsWindow.h b/widget/src/windows/nsWindow.h
index e41eb93f7ad2..94cc0ac0d003 100644
--- a/widget/src/windows/nsWindow.h
+++ b/widget/src/windows/nsWindow.h
@@ -387,7 +387,7 @@ protected:
 
 #ifdef MOZ_IPC
   static bool             IsAsyncResponseEvent(UINT aMsg, LRESULT& aResult);
-  static void             IPCWindowProcHandler(HWND& hWnd, UINT& msg, WPARAM& wParam, LPARAM& lParam);
+  void                    IPCWindowProcHandler(UINT& msg, WPARAM& wParam, LPARAM& lParam);
 #endif // MOZ_IPC
 
   /**