Just installed the new Fedora 15 on a 64-bit platform. After installing Flash 10 I had no sound on my bluetooth headset. After activating the bluetooth system which is deactivated by default after a new install, see my other article, I had to install the alsa-pulseaudio-plugin to get the audio working.
Do the following to get flash player audio working:
$> sudo yum -y install alsa-plugins-pulseaudio
Restart firefox and you should have audio (try YouTube).