Just in case anyone was wanting to try out the new beta of Firefox 2, here's how to make it portable.
If you would like to leave your current version unharmed, just make a copy of the Portable Firefox folder and call it something like PortableFirefox2.
To install the Beta:
1. go to the Mozilla FTP site, http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/bonecho-beta1-can...
and download the .zip version.
2. Unzip the file to the PortableFirefox (or PortableFirefox2) folder. If you're asked about overwriting files, click "yes".
Now you can use the portable Firefox launcher as you normally would to open the Beta. Happy Testing!