The script reference for Screen.fullScreen says:
My first question is, why not, since you can manually invoke fullscreen from the web player right-click menu and from a plugin call for widgets? Is is to prevent someone’s computer going fullscreen as soon as they browse onto an aggressive Unity web player?
My followup question is, if the variable is settable but ineffective in the web player, does that mean it can’t be used to detect if you’re in fullscreen mode? In other words, if you switch to fullscreen from the right-click menu, does that variable change?