Examine source code of Double-click pronounce

{
  "manifest_version": 2,
  "name": "Double-click pronounce",
  "version": "2.5.1",
  "description": "Never doubt how to pronounce a word. Better your spoken languages!",
  "icons": {
    "48": "icons/border-48.png"
  },
  "background": {
    "persistent": false,
    "scripts": [
      "browser-polyfill.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "browser-polyfill.js",
        "pronounce.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options.html"
  },
  "permissions": [
    "tabs",
    "storage",
    "management"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f8716d82-2c5c-430d-b783-5473310342cf}"
    }
  },
  "browser_action": {
    "default_icon": {
      "32": "icons/border-48.png"
    },
    "default_title": "Pronounce",
    "default_popup": "options.html"
  }
}