Examine source code of freepaper

{
  "name": "freepaper",
  "version": "2.1.0.4resigned1",
  "version_name": "freepaper 2.1",
  "manifest_version": 2,
  "description": "instant access to research papers by freepaper.me.",
  "icons": {
    "16": "img/icon-16.png",
    "32": "img/icon-32.png",
    "48": "img/icon-48.png",
    "64": "img/icon-64.png",
    "128": "img/icon-128.png"
  },
  "applications": {
    "gecko": {
      "strict_min_version": "53.0",
      "id": "{bd9321d9-1bc4-42fb-a755-d49caaa71f2e}"
    }
  },
  "browser_action": {
    "default_icon": "img/icon-32.png",
    "default_title": "freepaper",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "js/jquery-3.1.1.min.js",
        "freepaper.js"
      ]
    }
  ],
  "permissions": [
    "*://*.oadoi.org/*",
    "*://freepaper.me/*",
    "*://*.freepaper.me/*",
    "tabs",
    "storage",
    "activeTab",
    "contextMenus",
    "notifications"
  ],
  "externally_connectable": {
    "matches": [
      "*://freepaper.me/*"
    ]
  },
  "web_accessible_resources": [
    "freepaper.html",
    "/img/*"
  ]
}