Examine source code of Feature Queries Manager

{
  "manifest_version": 2,
  "name": "Feature Queries Manager",
  "short_name": "FQM",
  "description": "Manage and toggle CSS on a page behind a @supports Feature Query.",
  "version": "0.4resigned1",
  "permissions": [
    "tabs",
    "activeTab",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "browser-polyfill.js",
      "background.js"
    ]
  },
  "devtools_page": "devtools/index.html",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "browser-polyfill.js",
        "content/content.js"
      ]
    }
  ],
  "icons": {
    "16": "images/icon-white@16.png",
    "48": "images/icon-white@48.png",
    "64": "images/icon-white@64.png",
    "128": "images/icon-white@128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{18f7c9a9-5370-4060-9e77-07cb76c28f5e}"
    }
  }
}