--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -3985,16 +3985,22 @@ pref("mousewheel.system_settings_cache.f
 
 // High resolution scrolling with supported mouse drivers on Vista or later.
 pref("mousewheel.enable_pixel_scrolling", true);
 
 // If your mouse drive sends WM_*SCROLL messages when you turn your mouse wheel,
 // set this to true.  Then, gecko processes them as mouse wheel messages.
 pref("mousewheel.emulate_at_wm_scroll", false);
 
+// Some odd touchpad utils give focus to window under cursor when user tries
+// to scroll.  If this is true, Gecko tries to emulate such odd behavior.
+// Don't make this true unless you want to debug.  Enabling this pref causes
+// making damage to the performance.
+pref("mousewheel.debug.make_window_under_cursor_foreground", false);
+
 // Enables or disabled the TrackPoint hack, -1 is autodetect, 0 is off,
 // and 1 is on.  Set this to 1 if TrackPoint scrolling is not working.
 pref("ui.trackpoint_hack.enabled", -1);
 
 // Setting this to a non-empty string overrides the Win32 "window class" used
 // for "normal" windows. Setting this to MozillaUIWindowClass might make
 // some trackpad drivers behave better.
 pref("ui.window_class_override", "");

--- a/widget/windows/WinMouseScrollHandler.cpp
+++ b/widget/windows/WinMouseScrollHandler.cpp
@@ -441,16 +441,24 @@ MouseScrollHandler::ProcessNativeMouseWh
           ("MouseScroll::ProcessNativeMouseWheelMessage: Our window which is "
            "managed by nsWindow is not found under the cursor"));
         return;
       }
     }
 
     MOZ_ASSERT(destWindow, "destWindow must not be NULL");
 
+    // Some odd touchpad utils sets focus to window under the mouse cursor.
+    // this emulates the odd behavior for debug.
+    if (mUserPrefs.ShouldEmulateToMakeWindowUnderCursorForeground() &&
+        (aMessage == WM_MOUSEWHEEL || aMessage == WM_MOUSEHWHEEL) &&
+        ::GetForegroundWindow() != destWindow->GetWindowHandle()) {
+      ::SetForegroundWindow(destWindow->GetWindowHandle());
+    }
+
     // If the found window is our plugin window, it means that the message
     // has been handled by the plugin but not consumed.  We should handle the
     // message on its parent window.  However, note that the DOM event may
     // cause accessing the plugin.  Therefore, we should unlock the plugin
     // process by using PostMessage().
     if (destWindow->IsPlugin()) {
       destWindow = destWindow->GetParentWindowBase(false);
       if (!destWindow) {
@@ -1116,35 +1124,40 @@ MouseScrollHandler::UserPrefs::Init()
 
   mScrollMessageHandledAsWheelMessage =
     Preferences::GetBool("mousewheel.emulate_at_wm_scroll", false);
   mEnableSystemSettingCache =
     Preferences::GetBool("mousewheel.system_settings_cache.enabled", true);
   mForceEnableSystemSettingCache =
     Preferences::GetBool("mousewheel.system_settings_cache.force_enabled",
                          false);
+  mEmulateToMakeWindowUnderCursorForeground =
+    Preferences::GetBool("mousewheel.debug.make_window_under_cursor_foreground",
+                         false);
   mOverriddenVerticalScrollAmount =
     Preferences::GetInt("mousewheel.windows.vertical_amount_override", -1);
   mOverriddenHorizontalScrollAmount =
     Preferences::GetInt("mousewheel.windows.horizontal_amount_override", -1);
   mMouseScrollTransactionTimeout =
     Preferences::GetInt("mousewheel.windows.transaction.timeout",
                         DEFAULT_TIMEOUT_DURATION);
 
   MOZ_LOG(gMouseScrollLog, LogLevel::Info,
     ("MouseScroll::UserPrefs::Init(): initialized, "
        "mScrollMessageHandledAsWheelMessage=%s, "
        "mEnableSystemSettingCache=%s, "
        "mForceEnableSystemSettingCache=%s, "
+       "mEmulateToMakeWindowUnderCursorForeground=%s, "
        "mOverriddenVerticalScrollAmount=%d, "
        "mOverriddenHorizontalScrollAmount=%d, "
        "mMouseScrollTransactionTimeout=%d",
      GetBoolName(mScrollMessageHandledAsWheelMessage),
      GetBoolName(mEnableSystemSettingCache),
      GetBoolName(mForceEnableSystemSettingCache),
+     GetBoolName(mEmulateToMakeWindowUnderCursorForeground),
      mOverriddenVerticalScrollAmount, mOverriddenHorizontalScrollAmount,
      mMouseScrollTransactionTimeout));
 }
 
 void
 MouseScrollHandler::UserPrefs::MarkDirty()
 {
   MOZ_LOG(gMouseScrollLog, LogLevel::Info,

--- a/widget/windows/WinMouseScrollHandler.h
+++ b/widget/windows/WinMouseScrollHandler.h
@@ -348,16 +348,22 @@ private:
     }
 
     bool IsSystemSettingCacheForciblyEnabled()
     {
       Init();
       return mForceEnableSystemSettingCache;
     }
 
+    bool ShouldEmulateToMakeWindowUnderCursorForeground()
+    {
+      Init();
+      return mEmulateToMakeWindowUnderCursorForeground;
+    }
+
     int32_t GetOverriddenVerticalScrollAmout()
     {
       Init();
       return mOverriddenVerticalScrollAmount;
     }
 
     int32_t GetOverriddenHorizontalScrollAmout()
     {
@@ -378,16 +384,17 @@ private:
     {
       static_cast<UserPrefs*>(aClosure)->MarkDirty();
     }
 
     bool mInitialized;
     bool mScrollMessageHandledAsWheelMessage;
     bool mEnableSystemSettingCache;
     bool mForceEnableSystemSettingCache;
+    bool mEmulateToMakeWindowUnderCursorForeground;
     int32_t mOverriddenVerticalScrollAmount;
     int32_t mOverriddenHorizontalScrollAmount;
     int32_t mMouseScrollTransactionTimeout;
   };
 
   UserPrefs mUserPrefs;
 
   class SynthesizingEvent {