- Follow instructions: http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html
- Download and reinstall the latest version(s): http://www.adobe.com/products/flashplayer/distribution3.html
I would uninstall memory fox for starters. It is probably constantly flushing Firefox and the plugin container to the page file which would explain why Flash would stutter. Did you try safe mode?
The problem was that I my C: was pretty full. I was under 5 gb. That not only gave me streaming issues, but the whole OS was slowing down.