My web pages are being displayed without the Mozilla Firefox borders, and I cant view the applications, places and system bar on the top. I accidentally pressed some button and I cant get the default settings back. Can anyone help me out with this?
As Seth says, Firefox is probably in full screen mode. F11 both enters and leaves full screen mode. So try pressing F11. That's probably the button you pressed by accident; pressing it again should bring you back to normal windowed mode.