Examine source code of Speak Timer

{
  "manifest_version": 2,
  "name": "Speak Timer",
  "description": "Timer for monitoring the duration of a talk.",
  "version": "1.3",
  "icons": {
    "48": "assets/app-icon.svg",
    "96": "assets/app-icon.svg"
  },
  "browser_action": {
    "default_icon": "assets/app-icon.svg",
    "default_title": "Speak Timer"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "speak-timer@rt"
    }
  }
}