Is there a Facebook messenger app

I don't know if you're still looking, but here's your answer. It's not an official Facebook app, but I use it every day and I love it.

Here is the link to the site I used to download it

General way

So what about Empathy ?
Usually empathy is installed in Ubuntu when it comes. But if no go ahead install it from here. Or just click button

Note you can't write to offline person. But I think if you will have conversation already opened you can.

Alternative way

So here is alternative way: integrating facebook chat with firefox, read more here
And install plugin from here

Yes there is !

Here is an "un-official official facebook messenger" app.

You can download from here: http://messengerfordesktop.com