Examine source code of Manga Spread Merger

{
  "manifest_version": 2,
  "name": "Manga Spread Merger",
  "version": "0.0.1",
  "description": "A browser extension that helps manga readers join/merge two-page spreads into one in websites that don't do that.",
  "icons": {
    "16": "images/ext_icon/merge16.png",
    "32": "images/ext_icon/merge32.png",
    "48": "images/ext_icon/merge48.png",
    "128": "images/ext_icon/merge128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://mangaplus.shueisha.co.jp/viewer/*",
        "https://mangaplus.shueisha.co.jp/viewer/*"
      ],
      "js": [
        "src/contentscript.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "src/background.js"
    ]
  }
}