Examine source code of Page Timer by Ravi

{
  "manifest_version": 2,
  "name": "Page Timer",
  "version": "1.0",
  "description": "A timer that stops when the page is refreshed or changed.",
  "permissions": [
    "storage",
    "activeTab",
    "tabs",
    "webNavigation"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e9a2d754-874f-4185-8305-62b27913b535}"
    }
  }
}