Phosphore bêta 2 multi

Hello,
I know this question has been asked a hundred times, but I’ve never found what I was looking for. So here it is:

I’m trying to play multiplayer with a friend, but without success.
I found out how to do it on this site

 https://forums.commentcamarche.net/forum/affich-3924870-rasterwerks-multijoueur 

but I still can't manage it.

- Can you please tell me in detail how to set it up?

Thank you very much for your help

Configuration: Windows 7 / Firefox 5.0