Examine source code of How2Pronounce

{
  "manifest_version": 2,
  "name": "How2Pronounce",
  "version": "2.0.0",
  "description": "Pronunciation for American English words with phonetic IPA and audio",
  "icons": {
    "48": "icons/icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/content/bundle/messages.js"
      ]
    },
    {
      "matches": [
        "https://dictionary.cambridge.org/us/dictionary/english/*"
      ],
      "js": [
        "src/content/bundle/cambridge.js"
      ]
    },
    {
      "matches": [
        "https://howjsay.com/*"
      ],
      "js": [
        "src/content/bundle/howjsay.js"
      ]
    },
    {
      "matches": [
        "https://tophonetics.com/"
      ],
      "js": [
        "src/content/bundle/tophonetics.js"
      ]
    },
    {
      "matches": [
        "https://www.linguee.com/*",
        "https://www.linguee.com.br/*"
      ],
      "js": [
        "src/content/bundle/linguee.js"
      ]
    },
    {
      "matches": [
        "https://www.oxfordlearnersdictionaries.com/*"
      ],
      "js": [
        "src/content/bundle/oxford.js"
      ]
    }
  ],
  "background": {
    "page": "src/background/background.html",
    "persistent": true
  },
  "options_ui": {
    "page": "src/options/options.html"
  },
  "browser_action": {
    "default_icon": {
      "19": "icons/icon-19.png",
      "38": "icons/icon-38.png"
    },
    "default_title": "Pronunciation"
  },
  "permissions": [
    "https://www.google.com/",
    "https://ssl.gstatic.com/",
    "https://dictionary.cambridge.org/",
    "https://www.linguee.com/",
    "https://www.linguee.com.br/",
    "https://www.oxfordlearnersdictionaries.com/",
    "https://dictionary.cambridge.org/us/",
    "https://d1qx7pbj0dvboc.cloudfront.net/",
    "activeTab",
    "menus",
    "storage",
    "unlimitedStorage",
    "downloads",
    "alarms"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ba20300f-5408-4c06-95eb-7a2034365cee}"
    }
  }
}