Examine source code of Tab Count Icon

{
  "manifest_version": 2,
  "version": "0.12.1",
  "name": "Tab Count Icon",
  "description": "Shows number of open tabs.",
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "62.0"
    }
  },
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_icon": "icons/ic_tab_black_24px.svg"
  },
  "background": {
    "page": "background.html"
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": false
  }
}