Flat UI Colors - 280 handpicked colors ready for copy & paste
VivaldiFox - An add-on that allows colouring Firefox in a Vivaldi style fashion
Blend - Generate simple and beautiful CSS3 gradients.
automaticDark - Time-Based Theme Changer - Set Firefox to change the UI to a dark theme during the night and change back to a light theme during the day!
Hello Color - Color contrast generator
Dark Reader - Reduce eye strain in your browser with this extension that provides a dark theme for browsing.