When you enable "android private window visual refresh" in nimbus expirements you get a flame button on the left side of the toolbar instead of the home button. If you press the flame button all tabs will be closed in private mode. I like this feature but i now have enabled menu redesign and navigation toolbar in secret settings. It looks great but the flame button isn't anywhere to find with those option on so i hope mozilla will add the flame button somewhere on the toolbar to let people use both settings.