Examine source code of Search Ref Sources

{
  "manifest_version": 2,
  "name": "Search Ref Sources",
  "description": "Locate a journal article or a book by highlighting a reference, right-clicking and selecting a source to search (Amazon, arXiv, BASE, Crossref, Google Books, Google Scholar, Hollis, Library Hub Discover, Library of Congress, PubMed or WorldCat).",
  "version": "1.2",
  "developer": {
    "name": "pm"
  },
  "background": {
    "scripts": [
      "sources.js"
    ]
  },
  "permissions": [
    "contextMenus",
    "activeTab"
  ],
  "icons": {
    "78": "icons/ref78.png"
  }
}