YouTube Fullscreen Fit is a Firefox extension designed to optimize video playback in fullscreen mode. This tool allows users to stretch or zoom videos to fit their screen perfectly, accommodating various aspect ratios. Users can easily toggle the extension on or off using convenient buttons located next to the YouTube player. Additionally, the extension offers flexible settings, allowing for automatic activation or manual control over the video fitting process.

To utilize the full functionality of YouTube Fullscreen Fit, users must grant the extension permission to access YouTube after installation. The project is open-source, with its source code available for review on GitHub. This ensures transparency and the potential for community contributions, enhancing the overall user experience for those who enjoy watching YouTube videos in fullscreen.