Examine source code of HeaderTweaker

{
  "manifest_version": 2,
  "name": "HeaderTweaker",
  "version": "1.2.2",
  "description": "Lightweight browser extension that lets you easily modify outgoing HTTP headers",
  "content_security_policy": "default-src 'self'; font-src 'self' https://fonts.gstatic.com; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com;",
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "scripting",
    "activeTab",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "browser_action": {
    "default_popup": "headertweaker.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7f9e38fd-ff42-422c-bf5b-18d8edef0b17}"
    }
  }
}