As of 15 January 2018, this is the only add-on that will allow fullscreen functionality with no menu/nav bars on OSX 10.12.6 (FF 57.0.4). The browser.fullscreen.autohide function is broken for this machine configuration.

Feature request for this add-on: please add an icon that can be added to the menu bar that does the CTRL+SHIFT+F shortcut with one click.