Firefox blocks audio for other applications

[Mr.SpOOn]

Hi,
I have just installed an Ubuntu 9.10 64bit.

I use or, at least, I would like to use different audio applications,
for example: Renoise, Ardour, Hydrogen, Supercollider and so on.
At the moment I still haven't installed Jack, but this is not the
problem. Renoise can work fine without Jack and it works, indeed.

The problem is that if I first open Firefox and inside Firefox I watch
a video on youtube and only then I open Renoise, keeping Firefox open,
it finds the audio device busy and just doesn't work. But for example
I have no problem in using Rythmbox to listen to some music. So, why
this happens? Is there any way to have both Firefox and Renoise
working?

On a previous Ubuntu installation I had Jack installed. When I started
it I could just play music through it. So if I opened a video on
firefox, than Jack and Renoise (through Jack), Renoise worked, but I
couldn't here anything anymore from Firefox.

Any suggestion?

Thanks,
Carlo