Examine source code of Toggle web custom font

{
  "manifest_version": 2,
  "name": "Toggle web custom font",
  "version": "1.3",
  "description": "A toolbar button to toggle disabling web custom font (browser.display.use_document_fonts). Disabling it resists font fingerprint.",
  "homepage_url": "https://garywill.github.io",
  "icons": {
    "128": "icon.svg"
  },
  "developer": {
    "name": "Garywill",
    "url": "https://github.com/garywill/toggleWebCustomFont"
  },
  "permissions": [
    "browserSettings"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icon_btn.svg",
    "default_title": "Resist font fingerprint by disabling web custom font"
  },
  "commands": {
    "_execute_browser_action": {
      "description": "Click toolbar button"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{75d0437e-4f74-4d80-bf07-fc27c04ad3fd}"
    }
  }
}