Proper fullscreen mode only works if the flash itself has implemented a button for it but what you can do is open the swf file directly (URL should end with .swf) and then press F11 to fullscreen your browser.
Alternatively you can download the swf file and open it in the standalone flash player from Adobe, then press CTRL+F (or ALT+ENTER) to fullscreen, or via the menu: View > Full Screen
Using the adobe's standalone flash player offline also gives better performance than viewing the swf in your browser.
