Examine source code of Profile Indicator

{
  "description": "Displays which Firefox profile is in use.",
  "homepage_url": "https://addons.mozilla.org/firefox/addon/profile-indicator/",
  "manifest_version": 2,
  "name": "Profile Indicator",
  "permissions": [
    "theme",
    "storage"
  ],
  "options_ui": {
    "browser_style": true,
    "open_in_tab": true,
    "page": "options.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "version": "1.1"
}