Since Mozilla unveiled the "site specific browser" WebRunner, which loads a specific web app/site and only that w/o using much of a UI and relying on the web app to be the only user interface you need. Currently Mozilla has changed the name and has adopted the name Prism. And while I love the idea I can honestly say that I don't find it too practical making it portable. I'll be ready to back down on that should I be wrong, but for right now I find it highly unlikely.
This site here(in Spanish) made it portable but never once goes into the details of what was done.
So that means I guess I'll be going to the challenge of outdoing this person and providing details. That is of course if there is any major demand to do so, unless I feel it should be done just to do so.