FC10 i386, Firefox 3.5.3
Problem desc:
I'm having a problem with Firefox as I can see flash video, but can't hear anything. No sound. Or better to say I can hear it upon a fresh flash (re)install, but after restarting Firefox the sound disappears and won't come back since that action on. I aslo have a lot of plugins loaded (about

lugins)
I've just installed Seamonkey (1.1.18) and there's no flash trouble I faced with firefox.
My solution may not suit well for all though, but it's worth trying.