[Hardy] Sound in one application mutes sound in all other applications

[Cnyh]

Example: if I am watching a video with Totem movie player, put it on pause, and try to play a video on YouTube in Firefox, no sound comes from the YouTube video. I had no problems with this in Gutsy.

Software sound mixing is enabled in sound preferences, and sound playback options are all set on Autodetect. An Intel soundcard was detected by Hardware Testing.

[Cnyh (jobinv)]

Duplicate status wrong. Firefox does not crash, it becomes soundless, but plays normally otherwise.

[Duncan Hawthorne (duncan.hawthorne)]

the duplicate status is right.
installing the package libflashsupport fixes your problem but makes firefox crash a lot more, which is why it is not done by default. The fixing of flash sound is blocked by the crashes, so this is correctly a dupe.
the bug this is marked as a dupe of has a way to get flash working with sound without crashes