Examine source code of AdFreeTube for Firefox

{
  "description": "Skips YouTube video ads.",
  "manifest_version": 2,
  "name": "AdFreeTube",
  "version": "1.0",
  "homepage_url": "https://donovan.v6.rocks",
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "aftBlock.js"
      ]
    }
  ]
}