Examine source code of Enforce SafeSearch

{
  "manifest_version": 2,
  "name": "Enforce Safe Search (=Adult Filter)",
  "description": "Toggles the built-in filter on many search engines (see https://github.com/serv-inc/safe-search for a list of sites).",
  "version": "6.4.1",
  "author": "serv-inc",
  "homepage_url": "https://github.com/serv-inc/safe-search",
  "short_name": "Enforce Safe Search",
  "applications": {
    "gecko": {
      "id": "{b52acdad-e4a6-44da-afc9-9bd22572db99}"
    }
  },
  "icons": {
    "128": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js",
      "settings.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "google_safe_fallback.js"
      ],
      "include_globs": [
        "*google*"
      ]
    },
    {
      "matches": [
        "*://www.youtube.com/watch*",
        "*://www.youtube.com/"
      ],
      "js": [
        "youtube_safe.js"
      ]
    }
  ],
  "options_ui": {
    "page": "options.html"
  },
  "permissions": [
    "<all_urls>",
    "cookies",
    "storage",
    "webNavigation",
    "webRequest",
    "webRequestBlocking"
  ],
  "storage": {
    "managed_schema": "schema.json"
  }
}