Examine source code of FocusFlash

{
  "manifest_version": 3,
  "name": "FocusFlash",
  "version": "1.0",
  "description": "Sharpen your thinking with one deep question per day.",
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "permissions": [],
  "host_permissions": [],
  "browser_specific_settings": {
    "gecko": {
      "id": "focusflash@example.com"
    }
  }
}