--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -5190,21 +5190,17 @@ bool nsWindow::ProcessMessage(UINT msg, 
         ForgetRedirectedKeyDownMessage();
       }
       if (sJustGotActivate) {
         result = DispatchFocusToTopLevelWindow(NS_ACTIVATE);
       }
       break;
 
     case WM_KILLFOCUS:
-      if (sJustGotDeactivate || !wParam) {
-        // Note: wParam is FALSE when the window has lost focus. Sometimes
-        // We can receive WM_KILLFOCUS with !wParam while changing to
-        // full-screen mode and we won't receive an WM_ACTIVATE/WA_INACTIVE
-        // message, so inform the focus manager that we've lost focus now.
+      if (sJustGotDeactivate) {
         result = DispatchFocusToTopLevelWindow(NS_DEACTIVATE);
       }
       break;
 
     case WM_WINDOWPOSCHANGED:
     {
       WINDOWPOS *wp = (LPWINDOWPOS)lParam;
       OnWindowPosChanged(wp, result);