Don't spawn separate ediff frame as this conflict with my setting in Fvwm:
AddToFunc MyFuncFocusWindow
+ I FlipFocus
+ I WarpToWindow 50 50
DestroyModuleConfig FvwmEvent-NewWindow
*FvwmEvent-NewWindow: Cmd
*FvwmEvent-NewWindow: add_window MyFuncFocusWindow
AddToFunc StartFunction I Module FvwmEvent
AddToFunc StartFunction I FvwmEvent FvwmEvent-NewWindow
Refer to thread: http://permalink.gmane.org/gmane.emacs.help/86918