Examine source code of Docutracks Signer

{
  "manifest_version": 2,
  "name": "Docutracks Signer",
  "description": "Use this extension to digitally sign any pdf managed by Docutracks.",
  "version": "4.0.1",
  "permissions": [
    "activeTab",
    "nativeMessaging"
  ],
  "applications": {
    "gecko": {
      "id": "docutracks_signer@dataverse.gr"
    }
  },
  "background": {
    "scripts": [
      "index.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "jquery-3.3.1.min.js",
        "content-script.js"
      ]
    }
  ],
  "icons": {
    "16": "img/Sign_16.png",
    "48": "img/Sign_48.png",
    "128": "img/Sign_128.png"
  },
  "browser_action": {
    "default_icon": "img/Sign_16.png",
    "default_popup": "popup.html"
  }
}