Ubuntu on 64-bit does not support Flash in Firefox – there simply is no 64-bit-plugin from macromedia, and gnash isn’t that usable yet.
Here is a link in german on how to get firefox 32-bit running with Java and Flash:
However, I still had no sound, but :
helped, as long as there is no other KDE or Gnome app blocking the sound device. For that I’m still searching…