Mozilla is currently (finally) developing Firefox for the mobile platform. The code base is at version 1.9 and called Fennec. Some development pictures are out and they can be seen here.
It is also reported the Firefox Mobile will make its first alpha release on the surfboard Nokia 810 this week.
Firefox Mobile screens & info:
http://www.readwriteweb.com/archives screenshots_of_firefox_mobile_for_windows_mobile_finally_surface.php
Firefox Mobile for Nokia 810:
http://www.crunchgear.com/2008/10/10/firefox-mobile-to-be-tested-first-on-nokia-n810/
Firefox Mobile CEO statement:
http://blog.wired.com/gadgets/2008/10/mozilla-firefox.html
My current choice of browser for my Samsung SGH-i780 is the Opera Mobile 9.5 beta. I guess it is the best mobile browser currently out there. Chck it out at http://www.opera.com/products/mobile/