Those are two orthogonal concerns. A (theoretical) browser in full screen mode might or might not display UI elements/browser chrome. A windowed browser might o

Those are two orthogonal concerns. A (theoretical) browser in full screen mode might or might not display UI elements/browser chrome. A windowed browser might or might not display browser chrome. A chromeless windowed browser would look something like QuickTime in macOS, if that helps you; the window consists entirely of the playing video until you mouse over it.