Mostly I am looking for a Firefox browser app that I can put on a flashdrive that leaves nothing whatsoever on my Debian OS. I had one for Windows 7 but can't find one for Debian.
On Linux these are two separate things. Portable app -> static build (there's one available on mozilla.com). Leaves nothing on your system -> maybe create a profile on the flash drive, and load that when you want to put your history etc. on the drive. "'App virtualization" pretty much doesn't exist on Linux. The closest thing is Docker.IO, but that's exclusively geared towards servers. Edit: a more involved way of doing this (or having a whole portable system!) might be to create a chroot on your USB stick. But that - Requires invocation of root privileges on the host system to chroot in - Requires that the USB stick be formatted in ext4, XFS, or some other Linux filesystem (either that or the use of a formatted file used as a loop filesystem) - Requires dropping privileges from root before running anything in the chroot, otherwise you have yourself a nice security hole. It would probably also be possible to encrypt the USB stick, but again it would be rather involved. Still, I should look into this...