Comment 7 for bug 321586

Had the same problem, tried many many things, but thanks to despotakisch I got it solved:
- removed the old flash player using synaptic: searched for a package with name 'swfdec' and got rid of it
- then (re-)installed the flash 10 from the adobe website

Flash content is now happily playing music. In the PulseAudio Manager you can see a client with name 'Alsa plug-in [firefox]'.
With flash version 9, some client with 'Alsa' in the name did also occur, but instead of one, hundreds of them which crashed firefox.

Glad I got it sorted.