Examine source code of Modyfi

{
  "manifest_version": 2,
  "name": "Modify",
  "version": "1.0",
  "description": "removes unwanted contents from a website",
  "icons": {
    "48": "pen.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.stackoverflow.com/questions/*"
      ],
      "js": [
        "modify.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{4ad50b82-0e3e-42c4-af82-0c98411e3acf}"
    }
  }
}