Examine source code of Startled Reminder

{
  "manifest_version": 2,
  "name": "Startled Reminder",
  "version": "1.0",
  "description": "Reminds you to take a break if you stay too long on a page.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6a0f6c86-75e4-4e71-b02c-97e0ec6d3385}"
    }
  }
}