if it wasn't for the BRIGHT WHITE accents on the sidebar this would rock.
EDIT FOR CREATOR
its been a while, but i meant the text, and the highlights for buttons and things are all white, instead of a dark color. i too have also been looking for that and it is tied to the "background tabs" color, and i at one point found the cutoff for making them dark at "FF5000" but after a random update i guess they deemed that "too dark" and switched my menus back to being white, last i checked that cutoff was now at "#FF6040", and that was too bright for me so i edited my "userchrome" css file with some help from a kind redditor here is the end of the url to get to that post describing the hurdles i went through to get an actual dark theme, im sorry it took so long for me to reply, hope you see this.
/r/firefox/comments/nu2ext/help_please_this_is_driving_me_insane_ever_since/