Examine source code of Trello as a Sidebar

{
  "manifest_version": 2,
  "name": "Trello as a Sidebar",
  "description": "Displays a sidebar that lets your projects with Trello.",
  "version": "1.0",
  "applications": {
    "gecko": {
      "strict_min_version": "54.0a1"
    }
  },
  "icons": {
    "48": "icons/icon_48.png",
    "96": "icons/icon_96.png"
  },
  "sidebar_action": {
    "default_icon": {
      "48": "icons/icon_48.png",
      "96": "icons/icon_96.png"
    },
    "default_title": "Trello Sidebar",
    "default_panel": "index.html"
  },
  "permissions": [
    "storage",
    "tabs"
  ],
  "commands": {
    "_execute_sidebar_action": {
      "suggested_key": {
        "default": "Ctrl+Alt+X"
      }
    }
  }
}