Examine source code of Unseen Tab Indicator

{
  "author": "igorlogius",
  "homepage_url": "https://github.com/igorlogius/unseen-tab-indicator",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "160": "icon.png"
  },
  "manifest_version": 2,
  "name": "Unseen Tab Indicator",
  "permissions": [
    "menus",
    "<all_urls>",
    "tabs"
  ],
  "version": "1.1.3",
  "browser_specific_settings": {
    "gecko": {
      "id": "{3d7a7514-0409-45d0-8dc4-bd747fea208e}"
    }
  }
}