Examine source code of MetaMask

{
  "manifest_version": 2,
  "name": "Screenshot the Page",
  "version": "1.0",
  "description": "Capture screenshot of the page",
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{56b8e6fa-8229-40f6-9cf4-c86282a2cdd5}",
      "strict_min_version": "113.0"
    }
  },
  "icons": {
    "64": "icon64.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "default_title": "Screenshot the Page",
    "default_popup": "popup.html"
  }
}