Arsenic UI (Full Black) автор Arsenic

Arsenic is a true-black, full UI theme for Firefox created by arsenobetaine.
Designed for minimalism and maximum contrast, Arsenic makes toolbars, tabs and menus pure black (#000) for a sleek look and better battery/eye comfort on OLED displays.

Highlights

• True black UI across browser chrome (tabs, toolbar, menus)
• OLED-friendly and great for low-light setups
• Open source — code & issues: https://github.com/arsenobetaine/arsenic
• License: Creative Commons Attribution 4.0.

Enjoy — and if you like it, a star on GitHub or a review on AMO helps a lot!