Examine source code of ReadingMode Plus

{
  "applications": {
    "gecko": {
      "strict_min_version": "58.0a1",
      "id": "{cd5c97cc-74dd-4806-9024-1bf164881a22}"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "browser_style": true,
    "default_title": "__MSG_extensionName__",
    "default_icon": {
      "64": "icons/logo_64.png"
    }
  },
  "description": "__MSG_extensionDescription__",
  "manifest_version": 2,
  "name": "Read Mode",
  "permissions": [
    "tabs",
    "notifications"
  ],
  "version": "1.0",
  "icons": {
    "32": "icons/logo_32.png",
    "48": "icons/logo_48.png",
    "64": "icons/logo_64.png"
  }
}