Examine source code of Focus Mode Toggle

{
  "manifest_version": 2,
  "name": "Focus Mode Toggle",
  "version": "1.0",
  "description": "Toggle on a focus mode that dims everything on a webpage except for the selected text or element.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icons/icon.png"
  },
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{19df8e27-1da1-4fbe-8c72-66bbd61271c9}"
    }
  }
}