Under the assumption that if I find something annoying, someone else has found it annoying, I went looking for a Firefox browser plugin to block the automatic playing of Flash animations, and found FlashBlock. It puts a small button on the page where the animation would have appeared, which you can view the animation if you desire. One note: after you install the plugin, choose FlashBlock from the Tools->Extensions menu, and enable the plugin using Options before restarting the browser. It does not automatically enable itself when installed.