This is an early test release of the mobile version of Firefox called Fennec. It was built so new additions like better touch screen support and other features that are appropriate for mobile phones and other handheld devices could be added to the already popular architecture of Firefox. The current version is available only on one mobile device the Nokia n810, but if you are curious enough to check it out try the versions for Windows, Mac OSX and Linux.
Web link: Fennec
Download: Fennec alpha 1 for Windows