The button appears for me in the Crosswalk player app in preview-over-wifi, but pressing the button navigates to Twitter inside the app itself, replacing the game. That's not very helpful. I've tried hacking it to open a window the same way the Browser object does, but the Twitter API does something different that I can't figure out.
I think the easiest thing to do is just make your own ordinary button and use the Browser object's 'Open URL' action to open your feed's page on Twitter so the user can do whatever they want from there.