Examine source code of MasterKey

{
  "description": "Derivate your passwords from a secret key and the service name",
  "manifest_version": 2,
  "name": "MasterKey",
  "version": "1.0.1resigned1",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/borderify",
  "icons": {
    "48": "img/logo.png"
  },
  "browser_action": {
    "default_icon": "img/logo.png",
    "default_title": "MasterKey",
    "default_popup": "html/panel.html"
  },
  "permissions": [
    "activeTab",
    "contextMenus",
    "clipboardWrite",
    "storage"
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "js/content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "@masterkey"
    }
  }
}