Examine source code of A11yWidget

{
  "description": "Add-on allows users with disabilities easy and convenient way to browse most websites.",
  "manifest_version": 2,
  "short_name": "A11y Toolbox",
  "name": "a11ywidget",
  "version": "0.3",
  "icons": {
    "48": "icons/icon48.png"
  },
  "applications": {
    "gecko": {
      "id": "@a11ywidget",
      "strict_min_version": "57.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "js/saferInnerHTML.js",
        "js/content.js",
        "js/addwidget.js"
      ]
    }
  ],
  "permissions": [
    "activeTab",
    "storage"
  ]
}