Examine source code of Focus Mode

{
  "manifest_version": 2,
  "name": "Focus Mode",
  "version": "1.0",
  "description": "Highlight a specific element on the page and dim the rest.",
  "permissions": [
    "activeTab",
    "contextMenus"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d5f6cdeb-6e0c-44b2-b113-53c40bc6923b}"
    }
  }
}