Mozilla Firefox Portable is the portable version of Mozilla Firefox so you can take your Firefox anywhere you go preserving all your settings, add-ons, and more.
It has some specially-selected optimizations to make it perform faster and extend the life of your USB key and a specialized launcher that will allow most of your favorite extensions to work as you switch computers. It will also work from a CDRW drive (in packet mode), ZIP drives, external hard drives, MP3 players, flash RAM cards, etc.
To install Mozilla Firefox Portable, download and extract it to your USB drive's root directory. It will create a "Firefox" directory and all the requisite directories underneath. Then, to use Firefox on your drive, launch it with the executable in the Firefox directory.