Flash fullscreen slower than windowed "almost fullscreen"

[xandris]

When I play any flash animation (e.g. a YouTube video) in fullscreen mode, the performance is much worse than if I play the same animation in a window that's almost the same size as fullscreen. An easy way to do this is to open a video player page and tell Firefox to zoom in; the rectangle to which the video is mapped on the page becomes larger (this can actually exceed the dimensions of the monitor without any noticeable performance hit). Any idea why rendering to a rectangle on the page is so much faster than rendering fullscreen? Alternatively, know any magic environment variables for troubleshooting or a[/code] good profiler I can use to see where all this time is being spent?

Basic stats: