The Portable version is designed if you want to use Firefox on several computers and/or take it with you where ever you go.
It only downloads onto a USB Flash Drive but doesn't install onto the users computer, where the Full version of Firefox D/L's and installs onto the computer.
Being a Portable App
, it actually has all the features of the Full Version of Firefox.
So it really depends on your needs.
Edited by TMacK, 04 July 2007 - 05:35 PM.