try to add https always to the firefox. Prob will solve

That did not work

see if this is helpful : No audio when Flash video originates from an external site

thank you

Thanks. Already tried that. Didn't work.

Try to clear the Flash cookies (LSO).

Flash Website Storage Settings panel:

• http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html

Global Storage Settings Panel:

• http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager03.html

Flash Local storage settings Help:

• http://www.macromedia.com/support/documentation/en/flashplayer/help/help02.html

I'm having the same problem with Firefox 11 and Flash 11.2.202.228 on Windows 7. Flash works normally in both Chrome and IE, but I get no sound in Firefox. HTML5 videos play normally. I've tried all the above fixes with no luck.

I should add that, unlike the original poster, the problem started for me in Firefox 11, not 10. And as far as I can tell, it didn't happen following any Firefox or add-on updates.

I found this just now:

http://forums.adobe.com/thread/1026022

It fits the question, and I had the same problem. Their temporary solution for windows 7 was to lower the bitrate to 44100 KHz and that solved the problem for me. :) Figured I'd share.