Examine source code of HeaderTools - Inject and Edit Request Headers

{
  "manifest_version": 2,
  "name": "HeaderTools",
  "description": "A plugin for manipulating request headers",
  "version": "1.0",
  "browser_action": {
    "default_popup": "build/index.html",
    "default_icon": "htlogosq.png"
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "service/background.js"
    ],
    "persistent": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cf91c81a-285c-41ff-bb41-58cb538e68ff}"
    }
  }
}