Just wanted to post this issue I've had. Since installing Java and enabling in Firefox, sound (i.e., using xmms) only works until the java process is loaded (visiting a Java-enabled webpage). xmms errors that another process is using the soundcard and sound will not play. Regardless, sound does not work in any visited webpages (i.e., YouTube).
Essentially, once enabled, Java grabs the soundcard and won't let any other application use it.
Killing the java process allows xmms to reaccess the sound card, and sound works again, but killing the java process also kills Firefox.
If anyone can't duplicate this behavior I'd appreciate it, so we can assemble some data and work on a possible solution.