Examine source code of Keystroke Counter

{
  "manifest_version": 2,
  "name": "Keystroke Counter",
  "version": "1.0",
  "description": "Counts keyboard characters typed.",
  "permissions": [
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon-48.png"
    }
  },
  "icons": {
    "48": "icon-48.png"
  },
  "applications": {
    "gecko": {
      "id": "0xAmirreza@protonmail.com"
    }
  }
}