Are you using Media Player as a helper application for Flash? What happens if you just use Flash as a plugin with the browser?

Probably not related, but you have two VLC plugins. You might want to get rid of the older one.

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

• 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