Examine source code of Focus Mode

{
  "manifest_version": 2,
  "name": "Focus Mode",
  "version": "1.0",
  "description": "Blocks distracting websites to help you focus.",
  "permissions": [
    "storage",
    "webNavigation",
    "<all_urls>"
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Focus Mode",
    "default_popup": "popup/popup.html"
  },
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e965071f-9132-4aca-b38e-6a5c7daf545c}"
    }
  }
}