This setup requires the Sideberry extension. Click to install.
Some CSS is recommended for better colour coordination:
#root.root {--toolbar-bg: #1c1b22;}
#root.root {--frame-bg: #1c1b22;}
#root.root {--ctx-menu-bg: #1c1b22;}Add this to the Sideberry Styles Editor section: Sideberry Settings > Styles Editor.
Also go to about:addons > Sideberry > Run in Private Windows and select Allow.
The userChome.css file is based on One-line Firefox with heavy modifications and improvements and a disappearing bar option (disabled by default + has a very minor issue when in fullscreen).
The user.js file is based on Betterfox with SmoothFox Sharpen Scrolling, GPU accelerated canvas, and a reduced motion user preference.
The userContent.css file just removes some stuff from the new tab page.
Enjoy.