Hummingbird

The only tool you need to acquire English vocabulary as you go about your online routine.
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manifest.json
{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "__MSG_appName__",
  "description": "__MSG_appDesc__",
  "homepage_url": "http://example.com",
  "options_page": "pages/options.html",
  "background": {
    "page": "background.html",
    "persistent": false
  },
  "default_locale": "en",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "assets/icons/icon-16.png",
      "19": "assets/icons/icon-19.png",
      "32": "assets/icons/icon-32.png",
      "48": "assets/icons/icon-48.png",
      "128": "assets/icons/icon-128.png"
    },
    "persistent": true
  },
  "icons": {
    "16": "assets/icons/icon-16.png",
    "19": "assets/icons/icon-19.png",
    "32": "assets/icons/icon-32.png",
    "48": "assets/icons/icon-48.png",
    "128": "assets/icons/icon-128.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*",
        "<all_urls>"
      ],
      "js": [
        "js/content-script.bundle.js"
      ],
      "css": [
        "styles/content.styles.css"
      ]
    }
  ],
  "web_accessible_resources": [
    "styles/content.styles.css",
    "assets/icons/icon-48.png",
    "assets/images/*"
  ],
  "manifest_version": 2,
  "content_security_policy": "script-src 'self' 'unsafe-eval' https://www.google-analytics.com https://www.googletagmanager.com https://google-analytics.com; object-src 'self'",
  "version": "2.4.8"
}