Examine source code of ProtonMail (unofficial)

{
  "manifest_version": 2,
  "name": "ProtonMail (unofficial)",
  "version": "1.20.12",
  "description": "Unofficial ProtonMail extension. Provides notifications and makes it possible to close ProtonMail without getting logged out.",
  "homepage_url": "https://github.com/gitladen7/protonmail-webextension",
  "default_locale": "en",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "64": "icons/icon-64.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "https://mail.proton.me/*",
    "https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/*",
    "tabs",
    "storage",
    "cookies",
    "notifications",
    "webRequest",
    "alarms"
  ],
  "browser_action": {
    "browser_style": false,
    "default_popup": "index.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png"
    },
    "default_title": "ProtonMail"
  },
  "background": {
    "scripts": [
      "browser-polyfill.js",
      "background.js"
    ]
  },
  "content_security_policy": "default-src 'self'; connect-src https://mail.proton.me/api/events/ https://mail.proton.me/api/messages/count https://mail.proton.me/api/messages https://mail.proton.me/api/messages/read https://mail.proton.me/api/settings/mail https://mail.proton.me/api/auth/refresh https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/events/ https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/messages/count https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/messages https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/messages/read https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/settings/mail https://mail.protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/api/auth/refresh",
  "browser_specific_settings": {
    "gecko": {
      "id": "{70e827a1-4ae4-42e9-933b-66b817997082}"
    }
  }
}