This extension forces YouTube to open its player in the theater mode by default. You can simply switch back to the normal mode by pressing the button in the player, however, next time you open youTube it will be in the theater mode again! The extension does not have any options. It just works. Note that I am not using CSS or JS tricks to simulate theater mode. This is actual theater mode that YouTube offers. To have this option in the incognito mode, you need to allow extension to be active on this mode as well. For bug reports, use the discussion section of http://add0n.com/youtube-tools.html?from=theater --- My YouTube Enhancer Extensions:

YouTube use Flash Player
YouTube in HD (720p, 1080p, 1440p, 2160p)
YouTube no Annotations
YouTube no Buffer (no autoplay)
YouTube Stop AutoPlay Next
YouTube toggle Flash and HTML
YouTube Player AdBlocker
YouTube auto Pause and Resume
YouTube™ Stop Button
Theater Mode for YouTube (YouTube Wide Screen)

--- Note: After installation, the FAQs page of the extension opens once. This page has Google Analytics code. For more info please visit "Privacy Policy" section.