Examine source code of slip-fwdbwd

{
  "manifest_version": 2,
  "name": "swiape-fwdbwd",
  "version": "1.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "swipe@fwdbwd.js",
      "strict_min_version": "48.0"
    }
  },
  "description": "Adds forward and backward navigation from trackpad",
  "icons": {},
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "swipe-fwdbwd.js"
      ]
    }
  ]
}