The recent update to pulseaudio-0.9.21 looks like a dud. Brief sound effects play fine. But I have the gmail notifier Firefox plugin configured to play /usr/share/sounds/purple/login.wav, a slightly longer sound effect, as the new mail notification. After the pulseaudio update, Firefox gets through about 2 or three chimes, before Firefox freezes solid.
stracing the pulseaudio process shows that it's not doing anything. Killing the pulseaudio process unstucks Firefox. If, instead of killing pulseaudio I kill Firefox instead, the pulseaudio process pegs itself to 100% CPU. Bad karma.
Downgraded to pulseaudio-0.9.19, everything's ok now.
Weren't there a few intermediate releases of pulseaudio? The updates directory seems to keep only the most recent update of each package. I would've downgraded to the previous errata release, but there weren't none, so I had to roll back to the initial F12 package.
Someone else already reported pulseaudio breakage in bug 559032, but later followed up with a mea culpa thinking that it was his flash that was broken. But I do believe that there's a pulseaudio bug here, so I provided more info to reproduce this bug.