Examine source code of UAMasker

{
  "description": "Your User Agent is replaced by a random popular Firefox User Agent",
  "manifest_version": 2,
  "name": "UAMasker",
  "version": "1.0",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "scripts/background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "38": "icons/logo-active-38.png"
    },
    "theme_icons": [
      {
        "light": "icons/logo-active-38.png",
        "dark": "icons/logo-active-38.png",
        "size": 38
      }
    ],
    "default_title": "UAMasker"
  }
}