added note to Fx support info about SAMEORIGIN now cheking all ancestors (#867)
added note to Fx support info about SAMEORIGIN now cheking all ancestors (#867)


mdn/browser-compat-data,chrisdavidmills/browser-compat-data,teoli2003/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data