Examine source code of Planfix: Timer

{
  "manifest_version": 2,
  "name": "__MSG_application_title__",
  "description": "__MSG_application_description__",
  "version": "1.1.5",
  "default_locale": "en",
  "browser_action": {
    "default_icon": {
      "19": "images/extension-icon.png"
    },
    "default_popup": "index.html"
  },
  "icons": {
    "24": "images/128.png",
    "128": "images/128.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "https://*.planfix.ru/",
    "https://*.planfix.com/",
    "https://*.planfix.ua/",
    "storage"
  ],
  "background": {
    "scripts": [
      "js/debug.js",
      "js/common.js",
      "js/lib/date_format.js",
      "js/lib/jquery-3.4.1.min.js",
      "js/lib/url_parse.js",
      "js/settings.js",
      "js/storage.js",
      "js/timer.js",
      "js/planfix.js",
      "js/templates.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://*.planfix.ru/*",
        "https://*.planfix.com/*",
        "https://*.planfix.ua/*"
      ],
      "js": [
        "js/planfix_contentscript.js"
      ],
      "run_at": "document_end"
    }
  ],
  "content_security_policy": "default-src 'self'; object-src 'self'",
  "applications": {
    "gecko": {
      "id": "jid1-CbpoBAvAok3T8g@jetpack",
      "strict_min_version": "48.0"
    }
  }
}