Examine source code of KOSMOS Search

{
  "manifest_version": 2,
  "name": "KOSMOS Search",
  "version": "0.0.13",
  "description": "Through the context menu, this add-on retrieves KOSMOS, the online library catalog of Keio University, Japan. Select an ISBN or any keyword in the browser window and then bring up the context menu for the selected word (right-click the word in Windows OS). Move the cursor to 'KOSMOS Search' and click. Results shown in a new browser window.",
  "permissions": [
    "contextMenus"
  ],
  "background": {
    "scripts": [
      "index.js"
    ]
  }
}