Examine source code of Domain Filter

{
  "manifest_version": 2,
  "name": "Domain Filter",
  "version": "1.0",
  "description": "Removes specified domains in search results from Google and DuckDuckGo.",
  "permissions": [
    "storage",
    "tabs",
    "webRequest",
    "webRequestBlocking",
    "*://duckduckgo.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://duckduckgo.com/*"
      ],
      "js": [
        "content_filter.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "browser_action": {
    "default_popup": "options.html",
    "default_icon": {
      "16": "images/icon16.png",
      "48": "images/icon48.png",
      "128": "images/icon128.png"
    }
  },
  "icons": {
    "48": "images/icon48.png",
    "128": "images/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{61ed83b2-f2d7-479c-9d14-1b384c69d90f}"
    }
  }
}