Examine source code of TabScroller

{
  "manifest_version": 2,
  "name": "TabScroller",
  "version": "1.0.10.1",
  "applications": {
    "gecko": {
      "id": "{c7e8eb9e-a33a-4ad2-8fa8-89150d8c77f7}",
      "strict_min_version": "59.0"
    }
  },
  "description": "Scroll through tabs with the mouse wheel, while holding down the right button (and/or modifier keys).",
  "author": "Richard Antony Burton",
  "homepage_url": "https://github.com/raburton/tabscroller",
  "content_security_policy": "script-src 'self'; object-src 'self';",
  "permissions": [
    "storage",
    "browserSettings"
  ],
  "optional_permissions": [
    "tabs"
  ],
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "match_about_blank": true,
      "all_frames": true,
      "run_at": "document_start",
      "js": [
        "content.js"
      ]
    }
  ]
}