If you feel you have a sense of art in colors & like dark themes, Deep Dark FT for Firefox was one of the best add-ons & I like it, now in the new Firefox in Win 10 (New Versions) you have a dark theme but they are menus that still normal unless...if you apply dark mode (theme) in Win 10 you will get it for apps or desktop windows nowhere no fun part by doing this Firefox means and some default pages turn dark.