Question

Relevant things:

1. I had fullscreen code working before I did a security update on the flash player.
2. Nevertheless, I still can fullscreen Youtube right now
3. I’m doing the fullscreen activation in response to user clicks (therefore no security is blocking it AFAIK)
4. stage.displayState is null all the time, in the main timeline and even after assignments below.

Relevant code:

1) Set on the main timeline:

stage.scaleMode = StageScaleMode.SHOW_ALL; 
stage.align = StageAlign.RIGHT;

2) Set when a user clicks the fullscreen button:

import flash.display.*;
import flash.events.*;

/* ... */

this.addEventListener(MouseEvent.CLICK,modoFullScreen);

/* ... */

private function modoFullScreen(e:MouseEvent): void {
 try {
  stage.displayState = StageDisplayState.FULL_SCREEN;
 }
 catch (e:SecurityError) {
  trace(e.toString());  
 }
}

3) Set when a user clicks the normal screen button:

/* Similar as above, but then I set */
stage.displayState = StageDisplayState.NORMAL

Answer 1

Did you enable fullscreen when embedding?

To enable full-screen mode, developers must add a new and tag parameter, allowFullScreen, to their HTML. This parameter defaults to false, or not allowing full screen. To allow full-screen, developers must set allowFullScreen to true in their / tags.

http://www.adobe.com/devnet/flashplayer/articles/full_screen_mode.html