Welcome to Linux... you won't be sorry
When I first installed the flash player the sound would work... but it was delayed by a few seconds... very strange... and of course this sucked for watching homestarrunner
Then for un-related reasons, I un-installed Mozilla, then re-installed and re-added Flash Player. Now the sound is essentially fixed (it still feels a little sluggish after I've been running it for a while). So to answer your question(s), no, I haven't had the same problem you describe, but I have had sound troubles, and try uninstalling and reinstalling if possible.