TenFourFox was a web browser for Power Macintosh computers, based on Mozilla's Gecko layout engine. It is a port of Mozilla Firefox for PowerPC-based Macintosh computers running Mac OS X to retain compatibility with the older architecture and older versions of the operating system, and to add PowerPC-specific optimizations for improved performance. The project was started after Mozilla announced that it would not release Firefox 4 for PowerPC versions of OS X. Like Firefox, it includes compatibility with a wide range of addons, Acid2 and Acid3 compliance, and HTML 5 and CSS 3 features. It also includes JavaScript just-in-time compilation, custom builds for specific PowerPC processor families, and AltiVec acceleration of key media codecs. The primary maintainer is Cameron Kaiser.