Examine source code of Download icon

{
  "manifest_version": 2,
  "name": "download",
  "version": "1.0",
  "description": "Light blue cloud icon with a downward pointing arrow in the middle. The image represents the action of downloading data from the cloud or internet to the user's device.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f8266336-83be-4024-9427-647b7788c5b2}"
    }
  }
}