Examine source code of Bonfire Unread Count

{
  "manifest_version": 2,
  "name": "Bonfire Unread Count",
  "description": "Add unread notifications on Bonfire",
  "version": "0.1.4",
  "content_scripts": [
    {
      "matches": [
        "https://chat.meta.stackexchange.com/*",
        "https://chat.stackexchange.com/*",
        "https://chat.stackoverflow.com/*"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "images/icon16.png",
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "web_accessible_resources": [
    "injected_script.js"
  ],
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://chat.meta.stackexchange.com/*",
    "https://chat.stackexchange.com/*",
    "https://chat.stackoverflow.com/*",
    "https://cdn.sstatic.net/Sites/*"
  ]
}