Fullscreen is a achieve through the combination of flash and html settings.
Displaying flash as a fullscreen is one aspect but how you would control the contents placement in the flash is another aspect.
For example, following is a re-usable code for displaying .swf in fullscreen mode:
//stage scaling mode and alignment settings
Stage.scaleMode = 'noscale';
Stage.align = 'tl';
//setup the stage listener
stage_listener.onResize = onStageResize;
//code logic here will control the placement of the contents in the .swf file
in the html object and embed tags for the .swf file you would now set the width and height to 100%.