Works fine here on Linux.
It is a Flash Player that plays an MP3 file.

Do you see the player controls in the bottom frame?

Your above posted More system details list shows the Flash plugin, so that should be working.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

I have tried again to load my website www.thecausejams.com on firefox and it will not load the music player, I have tried to disable my McAfee firewall, that didn't work, The player works fine on IE8.