Examine source code of BookmarkletsIcon

{
  "manifest_version": 2,
  "name": "BookmarkletsIcon",
  "version": "1.0",
  "description": "Makes all your bookmarklets available from an icon",
  "homepage_url": "https://kryogenix.org/code/FirefoxBookmarkletsIcon",
  "icons": {
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "bookmarks"
  ],
  "browser_action": {
    "default_icon": "icons/icon-32.png",
    "default_title": "Bookmarklets",
    "default_popup": "list_bookmarklets.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ca6ccd31-9dfd-43f3-8db6-fa3a794025a2}"
    }
  }
}