Classic YouTube Design is a discontinued Firefox extension that aimed to recreate the traditional YouTube layout within the newer Polymer framework. This extension sought to provide users with an interface reminiscent of the old design, achieving about 85% similarity through custom CSS and JavaScript. However, it is important to note that due to the limitations of the Polymer structure, users should not expect performance improvements or a complete replication of the old design. The extension is free to use and falls under the multimedia category, specifically graphic and design.

Unfortunately, the development of the Classic YouTube Design extension has been halted due to dwindling demand and the complexities introduced by ongoing changes from Google. Users looking for similar functionality are directed to alternative extensions, which offer regular updates and improved dark mode support. While this extension was designed to enhance the YouTube experience for users who preferred the classic layout, its discontinuation means that it may not function as intended in the future.