Examine source code of Add request headers

{
  "manifest_version": 2,
  "name": "Add request headers",
  "version": "1.0.6",
  "description": "Add request headers",
  "icons": {
    "32": "icon-32.png",
    "48": "icon-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icon-32.png",
    "default_popup": "popup.html"
  },
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3a790f70-1cfd-4565-8cbc-7c26b67217d1}"
    }
  }
}