--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -575,28 +575,41 @@ EventStateManager::PreHandleEvent(nsPres
         // then fall through...
       case WidgetMouseEvent::eRightButton:
       case WidgetMouseEvent::eMiddleButton:
         SetClickCount(aPresContext, mouseEvent, aStatus);
         break;
     }
     break;
   }
+  case NS_MOUSE_ENTER_WIDGET:
+    // In some cases on e10s NS_MOUSE_ENTER_WIDGET
+    // event was sent twice into child process of content.
+    // (From specific widget code (sending is not permanent) and
+    // from ESM::DispatchMouseOrPointerEvent (sending is permanent)).
+    // Flag mNoCrossProcessBoundaryForwarding helps to
+    // suppress sending accidental event from widget code.
+    aEvent->mFlags.mNoCrossProcessBoundaryForwarding = true;
+    break;
   case NS_MOUSE_EXIT_WIDGET:
     // If this is a remote frame, we receive NS_MOUSE_EXIT_WIDGET from the parent
     // the mouse exits our content. Since the parent may update the cursor
     // while the mouse is outside our frame, and since PuppetWidget caches the
     // current cursor internally, re-entering our content (say from over a
     // window edge) wont update the cursor if the cached value and the current
     // cursor match. So when the mouse exits a remote frame, clear the cached
     // widget cursor so a proper update will occur when the mouse re-enters.
     if (XRE_GetProcessType() == GeckoProcessType_Content) {
       ClearCachedWidgetCursor(mCurrentTarget);
     }
 
+    // Flag helps to suppress double event sending into process of content.
+    // For more information see comment above, at NS_MOUSE_ENTER_WIDGET case.
+    aEvent->mFlags.mNoCrossProcessBoundaryForwarding = true;
+
     // If the event is not a top-level window exit, then it's not
     // really an exit --- we may have traversed widget boundaries but
     // we're still in our toplevel window.
     if (mouseEvent->exit != WidgetMouseEvent::eTopLevel) {
       // Treat it as a synthetic move so we don't generate spurious
       // "exit" or "move" events.  Any necessary "out" or "over" events
       // will be generated by GenerateMouseEnterExit
       mouseEvent->message = NS_MOUSE_MOVE;
@@ -1178,17 +1191,16 @@ CrossProcessSafeEvent(const WidgetEvent&
   case eMouseEventClass:
     switch (aEvent.message) {
     case NS_MOUSE_BUTTON_DOWN:
     case NS_MOUSE_BUTTON_UP:
     case NS_MOUSE_MOVE:
     case NS_CONTEXTMENU:
     case NS_MOUSE_ENTER_WIDGET:
     case NS_MOUSE_EXIT_WIDGET:
-    case NS_MOUSE_OVER:
       return true;
     default:
       return false;
     }
   case eTouchEventClass:
     switch (aEvent.message) {
     case NS_TOUCH_START:
     case NS_TOUCH_MOVE:

--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -1221,35 +1221,31 @@ bool TabParent::SendRealMouseEvent(Widge
 {
   if (mIsDestroyed) {
     return false;
   }
   event.refPoint += GetChildProcessOffset();
 
   nsCOMPtr<nsIWidget> widget = GetWidget();
   if (widget) {
-    // When we mouseenter the tab, the tab's cursor should become the current
-    // cursor.  When we mouseexit, we stop.
-    if (event.message == NS_MOUSE_ENTER_WIDGET ||
-        event.message == NS_MOUSE_OVER) {
+    // When we mouseenter the tab, the tab's cursor should
+    // become the current cursor.  When we mouseexit, we stop.
+    if (NS_MOUSE_ENTER_WIDGET == event.message) {
       mTabSetsCursor = true;
       if (mCustomCursor) {
         widget->SetCursor(mCustomCursor, mCustomCursorHotspotX, mCustomCursorHotspotY);
       } else if (mCursor != nsCursor(-1)) {
         widget->SetCursor(mCursor);
       }
-      // We don't actually want to forward NS_MOUSE_ENTER_WIDGET messages.
-      return true;
-    } else if (event.message == NS_MOUSE_EXIT_WIDGET ||
-               event.message == NS_MOUSE_OUT) {
+    } else if (NS_MOUSE_EXIT_WIDGET == event.message) {
       mTabSetsCursor = false;
     }
   }
 
-  if (event.message == NS_MOUSE_MOVE) {
+  if (NS_MOUSE_MOVE == event.message) {
     return SendRealMouseMoveEvent(event);
   }
   return SendRealMouseButtonEvent(event);
 }
 
 LayoutDeviceToCSSScale
 TabParent::GetLayoutDeviceToCSSScale()
 {