I’ve tested IE and Firefox so far, both of them capture certain keystrokes.
For example, in IE I can’t use “Escape” because it’s being captured by IE as the Stop Page command. Similarily, F1 is bringing up the browser help. Alt+ almost anything is being ignored. CTRL+R activates the page refresh command.
FireFox is a bit more friendly; I can use Escape, but CTRL+R still refreshes the page.