Examine source code of Focus Mode for Tabs

{
  "manifest_version": 2,
  "name": "Focus Mode for Tabs",
  "version": "1.0",
  "description": "Hide or close distracting tabs to help you focus.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icons/icon.png"
  },
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{d02d003d-15f5-4810-9963-c14a59de1d46}"
    }
  }
}