Examine source code of Show Only Text Mode

{
  "manifest_version": 2,
  "name": "Show Only Text Mode",
  "version": "3.0",
  "description": "Hide images and display only text content on websites",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "16": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "show-only-text@yourdomain.com"
    }
  }
}