Any idea why the full screen button no longer works when playing through facebook?

I have the same problem. The game slider works but the right side of the main page doesn't. I also get a list of games on that side but only the # of people playing them. There is a " collapse " icon there, also, so you can use it to get rid of the list of games. Then you are able to play in full screen. That's my workaround for it. I'm thinking it's a Facebook issue and / or a bad server.

I had the same problem with Chrome But the game is working perfectly with Firefox

Works fine for me. I play through FB on pc. Try closing and restarting the browser.