Examine source code of TypeReady

{
  "name": "TypeReady",
  "description": "Auto-focus the search box or first input on every page. Skip the click and just start typing. Works in iframes and Shadow DOM.",
  "version": "1.7.2",
  "manifest_version": 2,
  "browser_specific_settings": {
    "gecko": {
      "id": "typeready@ajexperience.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "tr_constants.js",
      "tr_logging.js",
      "tr_browser-adapter.js",
      "tr_storage.js",
      "tr_install-defaults.js",
      "tr_background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "tr_constants.js",
        "tr_logging.js",
        "tr_browser-adapter.js",
        "tr_storage.js",
        "tr_debug-bootstrap.js",
        "tr_common.js",
        "tr_extension-settings.js",
        "tr_focus-popup.js",
        "tr_input-classifier.js",
        "tr_input-interactability.js",
        "tr_input-selector.js",
        "tr_input-visibility.js",
        "tr_input-traversal.js",
        "tr_input-ordering.js",
        "tr_input-discovery.js",
        "tr_focus-actions.js",
        "tr_frame-coordinator.js",
        "tr_shortcut-hosts.js",
        "tr_vsc-detector.js",
        "tr_generic-shortcut-detector.js",
        "tr_key-injector.js",
        "tr_yield-handler.js",
        "tr_focus-handler.js",
        "tr_contact-prefill.js",
        "tr_content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "permissions": [
    "storage",
    "activeTab",
    "tabs"
  ],
  "browser_action": {
    "default_popup": "tr_popup.html"
  },
  "icons": {
    "128": "icon128.png"
  }
}