Control Center for YouTube

YouTube Control Center is a browser extension to control YouTube pages from a toolbar popup. You can pause, resume, stop, move to the next or previous tracks right from the popup without the need to switch to the YouTube tab. Note that if there is no open YouTube tab, by pressing the toolbar button, a new YouTube page is opened. When the player starts to playing the video, popup is ready.

Using this extension you can also control page layout as well as the player behaviours like:
1. Stop player from buffering media
2. Change quality to HD (HD2160p, HD1440p, HD1080p, HD720p)
3. Prevent the player from displaying annotations
4. Prevent the player from starting the next track when the current one is finished

For more info please visit:
http://add0n.com/control-center.html