The download verbiage on the portable Thunderbird say it will manage your email on your portable drive and "also" your hard drive. Does portable Thunderbird create a mirror directory on your hard drive with your email? If so, is there anyway to avoid this?
It says that you can take all your email, etc with you. You can easily copy your stuff into TB Portable from an existing TB install.
Sometimes, the impossible can become possible, if you're awesome!