Examine source code of MetaMask

{
  "manifest_version": 3,
  "name": "MetaMask",
  "version": "12.18.7",
  "icons": {
    "128": "icon-128.png"
  },
  "action": {
    "default_title": "MetaMask",
    "default_icon": "icon-128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "storage",
    "unlimitedStorage",
    "clipboardWrite",
    "activeTab",
    "notifications",
    "scripting"
  ],
  "host_permissions": [
    "<all_urls>",
    "file://*/*"
  ],
  "optional_permissions": [
    "webRequest",
    "webRequestBlocking"
  ],
  "content_security_policy": {
    "extension_pages": "script-src 'self'; object-src 'self'"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{814334d6-c8aa-4082-ad9e-118d8de81e73}",
      "strict_min_version": "115.0"
    }
  }
}