In about:config, set this option to false layout.css.visited_links_enabled (if missing, create it as a boolean) I disabled :visited coloring a long time

In about:config, set this option to false layout.css.visited_links_enabled (if missing, create it as a boolean) I disabled :visited coloring a long time ago and it hasn't caused any significant problems. It just took a few weeks to get used to the changed link colors.