Examine source code of Fast Signature

{
  "name": "Fast Signature",
  "version": "2.5.2",
  "description": "Signature electronique",
  "author": "Docapost Fast",
  "manifest_version": 3,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://demo-parapheur.dfast.fr/*",
        "https://parapheur.dfast.fr/*",
        "https://int-parapheur.dfast.fr/*",
        "https://integration.efast.fr/*",
        "https://recette.efast.fr/*",
        "https://www.efast.fr/*"
      ],
      "run_at": "document_start",
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "fastsigner@dfast.fr",
      "strict_min_version": "67.0"
    }
  },
  "permissions": [
    "nativeMessaging",
    "tabs"
  ],
  "icons": {
    "16": "icon_16.png",
    "48": "icon_48.png",
    "128": "icon_128.png"
  }
}