ARCHIVED: PROJECT REMOVED FROM ADDONS MOZILLA! 😢 see: #3 (comment)
DBFM is a Firefox browser plugin that adds a dark theme to https://messenger.com site.
Currently, the plugin is not developed much (except for fixing minor bugs) because the new Facebook page and application contain a dark theme. However, myself and many others are still using the old messenger page so people who want to report minor bugs or send PR with plugin improvements can do so in this repository.
The plugin was created without JavaScript to give users full privacy.
Link to plugin on firefox site: https://addons.mozilla.org/en-US/firefox/addon/darkbackgroundformessenger/