1. In Wavebox, open a new window (click on blue globe icon bottom-right)
  2. Paste "chrome://flags" into the address bar and navigate to that page.
  3. Type "global media controls" into the search box
  4. In the item that's then shown, select "Enable" from the drop-down menu
  5. Restart Wavebox
  6. The icon will then be displayed in the top-right corner.