Could you check whether Firefox is muted? On my system, I click the volume icon in the "notification area" of the Taskbar (also known as the tray) and then click a Mixer link. This shows the individual per-application volume controls. I have attached a screen shot for reference.

Thanks for responding. All my application volumes are wide open. I'm wondering if it's certain links that aren't working; i found one that was.

Some sites may be using a plugin (like Flash) while other sites may be using the built-in video or audio player. If you right-click the player, the last line of the context menu usually gives away the applicable plugin, if the site is using a plugin. Does that help narrow down the source of the problem?

not sure; this is one website I don't get sound on the first two videos, but do get on the bottom one:

http://aplus.com/a/high-school-valedictorian-plans-flash-mob-for-graduation?utm_medium=aolts&o=tsa01&icid=maing-grid7|main5|dl9|sec1_lnk3%26pLid%3D-313323894&so=USaaNUbZLoSxzLQHwcq76o&ref=ns&v=tsa01

Let me know if you get any sound in the first two.

Tks!

Just crashed, so let me see whether I can reconstruct...

There are three imgur boxes. The first two are animated GIFs, so it's normal those have no sound. The third one is something called GifV, which shows Unmute on the right-click menu but actually doesn't make any sound when I unmute it. These might not have sound, I'm not sure.

http://imgur.com/blog/2014/10/09/introducing-gifv/

Thank you! Obviously I was expecting sound out of something that doesn't have sound! Sorry for the bother!!