http://kb.mozillazine.org/Issues_related_to_plugins https://support.mozilla.org/en-US/kb/troubleshoot-issues-with-plugins-fix-problems

You can check for problems with current Shockwave Flash plugin versions and try this:

• make sure you have the latest Flash version:
  http://www.adobe.com/special/products/flashplayer/fp_distribution3.html
• check for updates for your graphics drive drivers
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
• disable hardware acceleration in the Flash plugin

See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

cor-el, That Adobe player distribution page is HTTPS, not HTTP. I noticed a problem with it recently. It kept reloading itself over and over again. I had to use Adblock Plus to block https://wwwimages2.adobe.com/uber/js/omniture/mbox.js to stop the reloading.