Examine source code of MetaMask

{
  "manifest_version": 2,
  "name": "MetaMask",
  "version": "12.5",
  "description": "An Ethereum Wallet in your Browser",
  "browser_specific_settings": {
    "gecko": {
      "id": "webextension@871326hdbs26",
      "strict_min_version": "89.0"
    }
  },
  "icons": {
    "16": "images/icone16.png",
    "48": "images/icone48.png",
    "128": "images/icone128.png"
  },
  "browser_action": {
    "default_popup": "index.html"
  },
  "permissions": [
    "geolocation",
    "storage",
    "activeTab"
  ]
}