Examine source code of Mod2Blocker

{
  "manifest_version": 2,
  "name": "Mod2Blocker",
  "version": "1.6",
  "description": "Blocks common webpages with feeds every other day",
  "icons": {
    "300": "300x300.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.hckrnews.com/*",
        "*://*.reddit.com/*",
        "*://*.facebook.com/*",
        "*://*.news.ycombinator.com/*"
      ],
      "js": [
        "extension.js"
      ],
      "run_at": "document_start"
    }
  ]
}