I'm trying to watch a sports highlight video on my 2011 Macbook Pro. I've got my computer set up to be about as fast as it can, apart from upgrading the 2.3 ghz processor - a solid state drive, 8GB of RAM and a large cache. I also closed all applications and tabs other than the tab with the video open. I've got a fairly fast Internet connection at home; for example Netflix videos stream fine.
However the video quality on Flash videos is really blocky - the audio is OK, but the video is not at all smooth, it will show the same frame for one second and then skip to a new frame, which makes video watching impossible. I know it's not a problem with the video, because it appeared smooth on a desktop PC with the same internet connection running the same browser (Firefox).
What could be the problem? What steps can I take to debug it?