Synopsis: Mozilla Firefox is an web browser that includes popup blocking, tabbed browsing, smart search and built-in download manager. Firefox Portable is a special build of Mozilla Firefox that is optimized for use on a USB key drive. It has some specially-selected optimizations to make it perform faster and extend the life of your USB key as well as a specialized launcher that will allow most of your favorite extensions to work as you switch computers.
Two other alternatives are Mobile Firefox (works even on read-only media such as CDROM and DVDROM), and X-Firefox.