I use NASA Night Launch.

• https://addons.mozilla.org/firefox/browse/type:2
• https://addons.mozilla.org/en-US/firefox/search/?q=dark&cat=2%2C0&appver=24.9&platform=windows

• https://addons.mozilla.org/en-US/firefox/search/?q=black&cat=2%2C0&appver=24.9&platform=windows

Pale Moon-hosted themes ∞

• https://addons.palemoon.org/themes/complete/darkness/

  • Oh my god that's bad.

• https://addons.palemoon.org/themes/complete/darkpitch/

  • Better than Darkness. I'd have to adjust my currently-selected tab colour chrome modification. The bookmarks bar is too high contrast for me. Straight black with white text is bad. Maybe grey text or more likely a less black background. The location bar has the same problem.

Other themes ∞

• https://addons.mozilla.org/firefox/addon/453336

  • The tabs aren't distinguished well.

• https://addons.mozilla.org/firefox/addon/369943

  • The tabs aren't distinguished well.