Hi!

I have Windows XP Professional with the latest Firefox (3.0.2) but the previous versions (3.0.0, 3.0.1) had the same problem. My sound card is working fine in games, mp3 players, video players, etc, but in Firefox / YouTube / anything other, there's no sound.
No error message appers, just no sound :/
Thanks for answering

If you go to Tools > Options > Applications, is there anything in that box?

Do you have Flash installed? https://addons.mozilla.org/en-US/firefox/browse/type:7 (https://addons.mozilla.org/en-US/firefox/browse/type:7)
Or http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash&P2_Platform=Win32

If you go to Tools > Options > Applications, is there anything in that box?

Do you have Flash installed? https://addons.mozilla.org/en-US/firefox/browse/type:7 (https://addons.mozilla.org/en-US/firefox/browse/type:7)
or Adobe Flash Player Download Center - Windows (http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash&P2_Platform=Win32)

There is a lot of associations in that tab, I can't see exactly flash.

I have tried downloading, uninstalling old flash player, installing new, restart Firefox, and no sound... tried the same with the secound one, but still no sound.. I have no idea, maybe the sound driver (Realtek HD) is the problem (?)

Do you get sound from YouTube videos in IE?

It would be very odd for one app not to use the hardware sound settings.

Have you tried simply reinstalling Flash as it sounds like this is what may well be causing your issue.
The associations clearly are incorrect/non-existent, but fine within IE.

Thanks all for the help, solved :)
The problem was with the crazy Realtek HD audio driver, which only play sound to the front panel, I think it use for 2ch playback, confusing... I'm going to buy a new sound card :D
The games using 5.1 sound output, that's why I hear it normally.