Examine source code of ModernBlue

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#2196f3",
      "tab_background_text": "#fafafa"
    }
  },
  "version": "2.0",
  "name": "ModernBlue",
  "manifest_version": 2,
  "description": "This is a theme I made to make firefox fit my desktop design. It mainly consists of the color \"blue 500\" as defined <a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/d8d49efb164d9905151a1efbfad56bd7946e6bad699b13301fdc9a1b30c87d03/https%3A//material.io/guidelines/style/color.html%23color-color-palette\">here</a>. There is still a little bit grey 50, but just to comply with googles material design thoughts."
}