No sound in Firefox on Ubuntu
For some reason I had no sound in Firefox under Ubuntu 9.04 after upgrading from 8.04 and 8.10. In all other applications the sound worked without any problems. After some research I found that the package flashplugin-nonfree-extrasound fixes the issue. You can install it with the following command.
sudo aptitude install flashplugin-nonfree-extrasound
Hope this helps someone out there.