If you havent used any firefox css scripts before you must go to "about:config" and turn on "toolkit.legacyUserProfileCustomizations.stylesheets". Then you can go to "about:profiles" on firefox and open the root directory of the profile by clicking on the "open folder" button to the right. After that create a new folder named "chrome" if there is no such folder in your profile root folder. Finaly copy all the files (except the readme.md) into the "chrome" folder and restart firefox