Examine source code of Signal icon

{
  "manifest_version": 2,
  "name": "Signal icon",
  "version": "1.0",
  "description": "The signal symbol is commonly used to indicate the strength or quality of a wireless connection, such as Wi-Fi, cellular, Bluetooth.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7433eebf-3688-48d5-96e3-63cdba166aae}"
    }
  }
}