Abrir Facebook

Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        String facebookUrl = "https://www.facebook.com";
        try {
            Intent i = new Intent(Intent.ACTION_VIEW);
            String facebookUrlScheme = "fb://facewebmodal/f?href=" + facebookUrl;
            i.setData(Uri.parse(facebookUrlScheme));
            startActivity(i);
        } catch (Exception e) {
            // Abrir o link no navegador se o aplicativo do Facebook não estiver instalado
            Intent i = new Intent(Intent.ACTION_VIEW);
            i.setData(Uri.parse(facebookUrl));
            startActivity(i);
        }
    }
});