Examine source code of heartrate

{
  "theme": {
    "images": {
      "theme_frame": "firefoxpersona.png"
    },
    "colors": {
      "frame": "#54001c",
      "tab_background_text": "#54002a"
    }
  },
  "version": "2.0",
  "name": "heartrate",
  "manifest_version": 2,
  "description": "inspired by \"Crime and Punishment\""
}