Examine source code of Referrer Switch

{
  "manifest_version": 2,
  "name": "Referrer Switch",
  "version": "0.3.1",
  "description": "Adds a button to the toolbar to enable / spoof / disable sending referer header.",
  "icons": {
    "48": "icon.svg"
  },
  "permissions": [
    "storage",
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": "disabled.svg",
    "default_title": "Referrer Switch"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{033d950a-38b9-4976-b19e-5f9ed7d78daa}"
    }
  }
}