Examine source code of Sidebox

{
  "manifest_version": 2,
  "name": "Sidebox",
  "version": "0.8",
  "description": "Instant email inboxes for signing up to things",
  "icons": {
    "64": "icons/64.png"
  },
  "permissions": [
    "storage",
    "*://sidebox.net/*"
  ],
  "browser_action": {
    "default_popup": "popup/index.html",
    "default_area": "navbar"
  },
  "content_scripts": [
    {
      "matches": [
        "*://sidebox.net/*"
      ],
      "js": [
        "content-scripts/login.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false,
    "type": "module"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d14ff9a0-f832-4850-bf07-6622d5c8c760}"
    }
  }
}