Examine source code of CORS for Me

{
  "manifest_version": 2,
  "name": "CORS for Me",
  "version": "0.3.8",
  "author": "yobukodori",
  "description": "Allow cross-domain xhr request by adding CORS headers to response.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "storage",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "util.js",
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "CORS for Me",
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/button-48-off.png"
    }
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true,
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "cors-for-me@yobukodori"
    }
  }
}