Examine source code of Website Rating

{
  "manifest_version": 2,
  "name": "Website Rating",
  "version": "1.2",
  "applications": {
    "gecko": {
      "strict_min_version": "48.0"
    }
  },
  "description": "Show different color on an icon to denote rating when you visit a website. (Note this application sends hostname of all your visited pages to https://flagdb.herokuapp.com/ for checking/updating!)",
  "homepage_url": "https://github.com/cshu/flagdb/tree/master/webext",
  "icons": {
    "48": "icons/48.png"
  },
  "permissions": [
    "*://flagdb.herokuapp.com/*",
    "storage",
    "tabs"
  ],
  "background": {
    "scripts": [
      "bg.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/init32.png",
    "default_title": "Website Rating"
  }
}