Examine source code of Fast forward and backward

{
  "manifest_version": 2,
  "name": "youtube-seconds",
  "version": "0.2",
  "applications": {
    "gecko": {
      "id": "asiesmeatrapaste@escine.com",
      "strict_min_version": "42.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}