Brilliant! This works on Firefox when other options failed to hide the nav bar and tabs. 1st Tap the window so the top bar isn't activated. Press Ctrl+Shift+F. Easy! Using a keyboard shortcut doesn't add an icon to a crowded address/search bar. Press Esc to return. Now I can view online tutorials that show videos on their webpage without the distracting top bars. The window gets bigger, so it's easier to see details. Thank you Trishul~!!!