After working for my high school over the summer a few years back, I got a lovely gift of a 128MB Bonzai USB 1.1 Mini-Drive (link to the USB 2.0 edition). I didn't use it much at first - I didn't really have much of a need to transport files from home. It was useful, sure, just not real often. Then I started using Mozilla what-was-then-Phoenix which suited me well but wasn't installed on every machine I used, especially at school. After a while I put what-was-by-that-point-Firebird on my drive and although it took a little while to load because of the sluggishness of USB 1.1, it worked very well after it was loaded. More recently (on the-hopefully-final-Firefox) I pondered the ability to keep my settings files on my USB drive rather than having a new settings file for every computer I plugged in to. After a little searching, I sorted through some bugnotes about the ability to specify the settings path but that hasn't been implemented yet. A link pointed me in the direction of this page which contains a plethora of interesting firefox tips as well as how to create a batch file to launch Firefox with different setting locations. Because I have a few different drives on my PC, I've created two batch files - one which specifies the drive letter H: for my desktop PC and one that uses F: for the vast number of PCs with the typical drive setup. Both are on the root of my drive and make things a hell of a lot easier. After following the instructions and opening Firefox with the batch file a few times (2 or 3), I had a working profile on my USB drive! I copied my settings from my PC's settings file and off I go with a mobile location for Firefox to store it's settings.

I recommend the process for anyone that runs Firefox off a USB drive. Creating the batch file wasn't even difficult. Startup time is less than 30 seconds and I can take my settings (stored passwords! entire bookmark files!) wherever I go.

Update: Thanks to Dan "The Man" for pointing the way to much more elegant solution by John Haller. You can find his Portable Firefox version on his website or on mozdev.org.