Examine source code of Copy As Text

{
  "name": "Copy As Plain Text",
  "description": "Browser extension that shows page plain text",
  "version": "3.0",
  "permissions": [
    "contextMenus",
    "activeTab",
    "clipboardWrite"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "cnt-script.js"
      ],
      "all_frames": true
    }
  ],
  "icons": {
    "16": "assets/icon_16.png",
    "128": "assets/icon_128.png"
  },
  "applications": {
    "gecko": {
      "id": "@copyastext",
      "strict_min_version": "57.0"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Show page plain text",
    "default_icon": {
      "16": "assets/icon_16.png",
      "128": "assets/icon_128.png"
    }
  },
  "manifest_version": 2
}