FireNes

Hi,
I installed firenes 1.0 on firefox 3.0.
When I double click on a game, a little window opens. It opens the game. The window has the focus but even if I press enter, ctrl, x, z, etc etc nothing happens.
When I press the right or down arrow, the window scrolls a bit but I can't play.
My pc run a win xp pro.
Can you help me?
Thanks!