Examine source code of Replace Google CDN

{
  "name": "Replace Google CDN",
  "version": "0.3.1resigned1",
  "manifest_version": 2,
  "icons": {
    "128": "icons/128.png"
  },
  "applications": {
    "gecko": {
      "id": "ReplaceGoogleCDN@mozilla.org"
    }
  },
  "description": "Replace Google CDN with USTC CDN.",
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "<all_urls>"
  ],
  "author": "https://github.com/justjavac",
  "homepage_url": "https://github.com/justjavac/ReplaceGoogleCDN"
}