Examine source code of Certificate Pinner

{
  "manifest_version": 2,
  "developer": {
    "name": "Heurekus",
    "url": "https://gitlab.com/heurekus/certificate-pinner-for-firefox"
  },
  "name": "Certificate Pinner",
  "description": "Pin TLS Certificates of Websites\n\nThis add-on allows to 'pin' TLS certificates via its toolbar icon, i.e. to store their fingerprints.\n\nWhenever a page is loaded and the connection is TLS encrypted, it compares the fingerprint of the presented TLS certificate to the one that is stored. If they don't match, the TLS authentication process is interrupted before any local secrets such as session cookies, passwords, etc. are sent to the server. A new tab is opened to show the user the new certificate which might be genuine or not. If accepted, the user can replace the old fingerprint with the new fingerprint.\n\nA new button in the browser's toolbar opens a pop-up menu to pin and un-pin page certificates and to get a list of all pinned certificates.",
  "version": "0.17.10",
  "browser_action": {
    "default_icon": {
      "32": "icons/icon-32.png"
    },
    "default_title": "Cert-Pinner",
    "default_popup": "/popup/popup.html",
    "browser_style": true
  },
  "options_ui": {
    "page": "/options/options.html"
  },
  "permissions": [
    "notifications",
    "tabs",
    "activeTab",
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "32": "icons/icon-32.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9550e8a6-7884-43d1-ba9c-2c2928ab0a26}"
    }
  }
}