Examine source code of Enable Copy

{
  "manifest_version": 2,
  "name": "Enable Copy",
  "version": "1.0",
  "description": "Enables copying on websites that prevent it.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Enable Copy"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{1261b094-7fe9-48a4-afc1-f23134cc28c9}"
    }
  }
}