Theme for firefox using css userChrome.css feature, made in version 70.0
Go to about:support in firefox, open profile directory, create a new folder names chrome and paste the userChrome.css file into it. Enable toolkit.legacyUserProfileCustomizations.stylesheets in about:config.
Place a flexible space on both sides of the url bar;
Select the default firefox dark theme under themes;
Place the bookmarks in the same bar as the tabs (To do this right click -> customize and drag Bookmarks Toolbar Items to tab bar);
On Windows change default monospace font or change font in css, the default of windows is very unclear.