Examine source code of Visited Link Toggler

{
  "manifest_version": 2,
  "name": "Visited Link Toggler",
  "version": "14.0",
  "description": "Hover any link and press Ctrl+Alt+G (or Alt+Click) to toggle it between greyed-out (visited-looking) and unvisited. Un-visiting also removes the link's browser history entries and restores its true unvisited styling instantly. Toggles persist across pages, tabs, and sessions.",
  "permissions": [
    "storage",
    "history",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle",
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "visited-link-toggler@burnie",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}