Examine source code of Coal icon

{
  "manifest_version": 2,
  "name": "Coal icon",
  "version": "1.0",
  "description": "The coal symbol is often represented by an image of a rough, black rock, possibly with crystal-like facets (since coal is a partially crystallized form of carbon).",
  "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": "{a74e7d04-74b0-4c13-a995-5c103f9ba5e4}"
    }
  }
}