Turn Off the Lights for Firefox will fade entire page to dark while there is video playing on a webpage, so you can watch the video as if you were in the cinema.

• Turn the lights back on, by clicking on it
• Support multiple video sites: YouTube, HTML5 video,... and more
• Customize your YouTube:
• Auto HD: Set videos to play in HD automatically. Users can select from highres > 1080p > 720p > 480p > 360p > 240p > 144p > default
• Auto Wide: Automatically plays the video on the widest mode
• ... and more
• Easter Eggs:
• Shortcut key: T -> Do you like a real movie theater feeling?
• Option to make the screen dark when the user clicks on the play button
• Option to turn on/off the fade in and fade out effects
• Custom colors
• Option to Flash Detection
• Option to Show Dimness Level Bar
• Option Eye Protection for when it' s night. And with whitelist/blacklist filter
• Option atmosphere lighting that shows a glow around the video player
• Option to show the dark layer on the top of the window
• Options to shortcut keys:
  
  • Ctrl + Shift + L to toggle the lights
  • Alt + F8 to restore the default opacity value
  • Alt + F9 to save the current opacity value
  • Alt + F10 to enable/disable the Eye Protection feature
  • Alt + (arrow up) to increase the opacity
  • Alt + (arrow down) to decrease the opacity
  • Alt + * to toggle the lights on all open tabs
• Option Camera Motion
• Option Speech Recognition
• Option to place the Night Mode switch to toggle YouTube? in black or white theme. And with whitelist/blacklist filter
• Time stamp: Activate the Night Mode within the chosen time
• Blackout: Dims the web page and activates the Night Mode
• Option to stop YouTube and HTML5 videos from automatically playing.
• And More...