Examine source code of WhereIs

{
  "manifest_version": 2,
  "name": "WhereIs",
  "version": "1.1",
  "description": "The plugin adds a context menu to geocode and display on the map in the sidebar the Address/location/POI from the text selected by the user on the page.",
  "permissions": [
    "contextMenus"
  ],
  "icons": {
    "48": "icons/map_48.png",
    "96": "icons/map_96.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "sidebar_action": {
    "default_title": "Show on Map",
    "default_panel": "sidebar/sidebar.html",
    "default_icon": "icons/map_96.png",
    "open_at_install": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{391193d9-0694-4602-8aa3-6323041c4ed0}"
    }
  }
}