Examine source code of Content Scaler

{
  "manifest_version": 2,
  "name": "Content Scaler",
  "description": "This extension scales HTML content if the width of viewport was fixed.",
  "version": "1.0.8resigned1",
  "icons": {
    "16": "image/icon/16.png",
    "64": "image/icon/64.png"
  },
  "page_action": {
    "default_icon": "image/icon/16.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://*/*",
        "http://*/*",
        "file://*/*"
      ],
      "exclude_matches": [
        "https://www.smbc-card.com/*"
      ],
      "js": [
        "js/jquery-3.2.1.min.js",
        "js/content_scripts.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{433e6462-91e0-44b4-a3f4-2096af168865}"
    }
  }
}