Examine source code of Focus Mode

{
  "manifest_version": 2,
  "name": "Focus Mode",
  "version": "1.0",
  "description": "Enables focus mode by hiding distractions on webpages.",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Toggle Focus Mode"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "focus_mode.js"
      ],
      "css": [
        "focus_mode.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{4443b107-b8b1-4d34-8427-3444160cd349}"
    }
  }
}