Window Fullscreen for YouTube gives YouTube a real windowed-fullscreen mode. The player fills your browser window without going OS-level fullscreen — perfect for ultrawide monitors, dual-screen setups, or anyone who wants a bigger player while keeping the rest of the browser usable. Features

Native player button right next to YouTube's own fullscreen icon — not a toolbar popup, not a floating widget
Configurable hotkey (default Shift+F), Esc to exit
Auto-toggle on new videos (optional)
Scrollable mode — keep the player large and still reach comments below
Hover-to-reveal masthead so the search bar is always one mouse-flick away
Live chat side-panel with a draggable resize handle — choose sticky chat (pinned to right) or scroll-with-the-page
Granular hide controls for masthead, sidebar, comments
Native YouTube integration — three settings live inside YouTube's gear menu, styled to match

Why free? The most popular extension for windowed-fullscreen moved its core features behind a paywall, and the community wasn't happy. This extension ships every previously-paid feature free, source available for inspection. No paywall. No subscription. No nag prompts. Open source under MIT. Privacy This extension only accesses youtube.com. It stores settings in your browser's sync storage. It does not collect, transmit, or sell any data. Source code Github Repo