Google recently began forcing Chrome users to use the HTML5 player on YouTube. Google has also began doing this on Safari, starting with Safari 8. This also has the side-effect of interfering with ClickToPlugin's scripts. To switch back to a Flash player, go to Preferences -> Advanced -> enable "Show develop menu...". Now go to Develop -> User Agent -> Safari 7.1. You should now be getting the Flash player. If you're still getting the HTML5 player, go here and request the Flash player.