First public release.

FullScreen Theater Mode expands YouTube's theater mode (press T) to fill the entire browser viewport below the header — edge-to-edge with no side gaps — while always preserving the video's aspect ratio with automatic black bars. Works with 16:9, 4:3, ultrawide and vertical videos at any window size. Title, comments and suggestions move below the fold; scroll down to reach them. Includes a toolbar popup to toggle the enlargement and an auto-theater option. No data collection, no network requests; content scripts run only on youtube.com.