Examine source code of Custom Header Values

{
  "manifest_version": 2,
  "name": "Custom Header Values",
  "version": "1.6",
  "description": "Adds Header Values to requests if a matching URL is found.",
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  },
  "options_ui": {
    "page": "options.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f108ecb4-7615-48f6-88f6-2e3878c9a700}"
    }
  }
}