Comment 13 for bug 374407

I have found a work around that works for me:

Description: When amarok is runing and Firefox 3 tries to play a video with sound, no sound plays, and after closing firefox, it is hung in the background and must be killed.

Assumptions: Both Firefox and Amarok were trying to directly access my sound hardware causing an error. In my case it is listed in KDE system settings as: HDA Intel (AD198x Analog)

Workaround: Go to KDE System settings, Multimedia, Device Preference tab and set PulseAudio as the preferred (top) Output Device for all types of audio.

Tested working: Play a song in Amarok and also a youtube video in Firefox 3. Both applications can now play audio simultaneously and firefox does not hang after viewing the video. It can be closed cleanly.