You're welcome Chris
Ensure that you run the portable launcher for them (firefoxportable.exe) as this will keep it contained.
@DavidR,
It is exactly the same as a normal build, except that things like the cache, and other space taking option are disabled. It also installs to a folder, which it where everything is contained. Running the portable launcher (IIRC) places the relevant files where they belong until it is closed, and then it takes everything back and leaves it as before.
Currently, I have opted to use this as my preferred way of installing things...I have the portable versions of Firefox, Thunderbird, foxit, VLC, Notepad++ and a few other unofficial test releases...