no sound - browser plugins

[Roger Searle]

Hi, kubuntu feisty.  Sound generally works in that I can use amarok to 
play MP3s.  Yet I have no sound trying to view something like a YouTube 
video in a player embedded in a web browser.  And the "Test Sound" 
button in System Settings doesn't produce any sound. Audio device is 
ASLA, full duplex.

Googling hasn't given me any clarity or success eg installed 
libflash-mozplugin, have installed all codecs and plugins available in 
Automatix (flash, mplayer, firefox, multimedia codecs). 

What/where do I need to be looking for/at?
Cheers,
Roger