The upper case "Window.open" is a helper function of ours, it has this structure:
Window.open(url, name, width, height, scrollbars, resizable)
so your call need not specify "scrollbars", "width" and "height", use this instead:
CODE
Window.open('<%Product.EmailAFriendUrl%>', 'EmailAFriend',300,300,0,1)
(300x300, no scrollbars, resizable)