YouTube adds a settings option in video quality context menu in videos
Google owned video sharing service YouTube already has a settings page for registered users where they can tell the service what quality videos to play by default.
YouTube has now made it easier for users to set this setting from any video on the YouTube service.
Just click on the video resolution option on the video to get to the settings option.
One of the better settings is named:
Always play HD when switching to fullscreen (when available)
This would force the player to switch to HD mode if available on full screen view. HD videos are best viewed in full screen.
YouTube does not recommend running HD videos in regular sized window as it puts extra load on the machine.