Examine source code of Carbonalyser

{
  "manifest_version": 2,
  "name": "Carbonalyser",
  "description": "Analyse Internet usage carbon footprint",
  "author": "TheShiftProject",
  "version": "1.2.0",
  "icons": {
    "48": "icons/icon-on-48.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "script.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_popup": "popup/popup.html",
    "default_icon": {
      "48": "icons/icon-off-48.png"
    }
  },
  "default_locale": "en"
}