Mobile site doesn't work

I have a sample site I'm playing with (preparing for the real thing).
I have 4 articles in 2 different languages. They are associated with each other and things seems to work.
I've installed mobile joomla to create a mobile version of this simple site. Installation went ok but it seems to do nothing.
I access my site with firefox (using modify headers with Samsung S3 user agent) and all I can see is the desktop site.
I've looked around the settings but I don't understand why it's not working.

Can you help?

EDIT: I have the latest version of MJ with Joomla 3.1

Yes, eventually, without explanation, it started to work.
Thanks.