Examine source code of CheckThemAll

{
  "manifest_version": 2,
  "name": "CheckThemAll",
  "version": "1.6resigned1",
  "default_locale": "en",
  "description": "CheckThemAll allows you to quickly check/uncheck/invert all the checkboxes contained in a selection",
  "homepage_url": "https://github.com/SalvatoreMeschini/CheckThemAll",
  "applications": {
    "gecko": {
      "strict_min_version": "56.0",
      "id": "{ef462a4f-5c3a-4781-a453-23ad6fb08fd1}"
    }
  },
  "background": {
    "scripts": [
      "src/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/content-script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "options_ui": {
    "page": "src/settings.html"
  },
  "permissions": [
    "menus",
    "activeTab",
    "contextMenus",
    "notifications",
    "storage",
    "tabs",
    "<all_urls>"
  ],
  "icons": {
    "16": "icons/16x16.png",
    "32": "icons/32x32.png",
    "48": "icons/48x48.png"
  }
}