Examine source code of HostHeader

{
  "manifest_version": 2,
  "name": "HostHeader",
  "version": "1.0",
  "description": "The Host Header is sent in the HTTP request. All others headers are removed as possible.",
  "author": "katchov",
  "icons": {
    "64": "hostheader.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "hostheader@katchov"
    }
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}