UPDATE:
Turn Off the Lights support Firefox v52, see the download link on this page:
https://addons.mozilla.org/en-US/firefox/addon/turn-off-the-lights/versions/

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Hi there,

Do you use any other Firefox extensions? Have you tried to disable those one by one except Turn Off the Lights and then restart your Firefox web browser?

Please for questions or need help use next time the support form on this page:
https://www.turnoffthelights.com/support

Thanks,
www.turnoffthelights.com