Just recently after some update I found that the while playing the flash-videos in firefox (I do not know about other browsers!!) I can not hear any sound. Then I googled arround the web — unfortunately some of the solutions were wiered!!! or only for MS stuffs …. Here is what I did to get the sound back on my Fedora 9 machine —-

yum install libflashsupport

Ofcourse you have to be root to use yum on Fedora. Thanks to fedoraForum for the solution.