Examine source code of Keep in

{
  "name": "Keep in",
  "version": "1.0",
  "description": "Build an Extension to save Linkedin messages!",
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.linkedin.com/messaging/*",
        "https://www.linkedin.com/feed/"
      ],
      "js": [
        "message_page.js",
        "main_page.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "icons8-messages-50.png",
    "default_popup": "popup.html",
    "deafult_title": "Keep in Messages"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "https://www.linkedin.com/messaging/*",
    "https://www.linkedin.com/feed/"
  ],
  "manifest_version": 2
}