Examine source code of Recent Visit Overlay

{
  "manifest_version": 2,
  "name": "Recent Visit Overlay",
  "version": "1.0",
  "description": "Shows previous visit time.",
  "permissions": [
    "history",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "recentvisit@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}