a. Ultra lite Addon for Firefox.
b. Automatically sets a Dark theme for all YouTube pages.
c. Supports both HTML5 and Flash YouTube players.
d. Has an in-page switch button (at top right corner in YouTube website) to turn the dark theme ON or OFF.
e. Has 2 dark themes. Theme (A) uses standard CSS techniques to darken the YouTube page. Theme (B) uses CSS filters to do this job. For some unknown reasons in Firefox, theme (B) makes YouTube videos to become slow (only for latest versions of Firefox; this might be fixed in future updates). When you install the Addon, the default theme is A, which works fine with no issues. But, if you want to switch to theme B, please make sure the videos are playing normal.
Note 1: support page for this addon contains Google Analytic. Terms of service can be found at https://www.google.com/analytics/terms/
Note 2: in order to submit bugs, please visit addon's Homepage and fill the Bug report form.