I wonder how difficult it'd be to build a fullscreen browser replacement and have it load automatically. The fake browser could mimic real browser actions and easily mask the url (and all of the browser chrome, for that matter) and inject their own content when a user navigates to an interesting site. All the normal "safe" markers (e.g. green URL bar, security lock on the bottom right, the correct URL) could be shown to the user.
It would probably be too much work for too little payoff to actually make a browser that rendered to canvas, but they could do it for a couple of major target sites like gmail and banks.
But once you're full screen, F11 does indeed get you back to the original state. So I still don't see why ESC is needed.
The main reason is that you probably got into full-screen by pressing a button, not the F11 key, and now you just want a "get me out of this" key which escape is better for.
Although you would be breaking the standard convention.
fullscreen button is bottom right, when the level loads.
Nothing happens when I click the button.
EDIT: on Firefox too.
When is there ever going to be a download API?
* Command/, (going into Preferences disables it)