Comment 11 for bug 196470

Yep. I hadexactly the same problem. It is fixed, but only when you install fixes on new, empty os..

So for you there is an advice - reinstall pulseaudio and libflashplugin support for ex this way : apt-get install --reinstall pulseaudio libflashsupport
Second thing is to change everything to pulseaudio in "system->preferences->audio settings".

I'm just after those operations and now audio works fine even in flash r48 under Opera and on r115 under Firefox 3.

You have to know that flash is closed commercial software with MANY bugs. One of this bug`o`features is usage of ESD daemon to play sound.
libflashsupport is a wrapper to pass through flash sound to pulseaudio server so it's good to have it installed.