Examine source code of Custom Style

{
  "manifest_version": 2,
  "name": "Custom Style / Custard",
  "version": "0.4",
  "description": "Prototype to fix CSS styling of some websites.",
  "icons": {
    "48": "icons/custard-plain-svg.svg",
    "96": "icons/custard-plain-svg.svg"
  },
  "applications": {
    "gecko": {
      "id": "{0943784d-9004-4d2d-b006-2032997bc24d}"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "browser_style": true,
    "open_in_tab": true,
    "page": "extension.html"
  },
  "permissions": [
    "<all_urls>",
    "tabs",
    "storage"
  ]
}