I often use the F11 trick for games which doesn't fit in a single screen.
For full screen... With Flash, let's just say that unless you have an incredibly fast computer you don't actually want to do that. It would get quite laggy.
Seeing as there's nothing but "Press F11" posts coming into this thread (which have all been deleted) and the topic seems to be answered, I think it's time to grab the padlock. =)