grml live

You won't find Grml in the top 100 of DistroWatch's Page Hit Ranking, but this distro has been around since 2004. Based on Debian Testing, Grml can be run live from a flash drive and ships with loads of system administration tools. It comes with the Fluxbox window manager rather than a full-featured desktop environment, and you'll get mc and nano instead of a fancy GUI file manager and text editor, but Firefox ESR is included.

I downloaded the grml64-full_2017.05 iso (the download was only about 600 MB), used dd to put it on a flash drive, and booted up, with no problems. Not much to the default setup:

Here's a shot with the right-click desktop menu opened up:

Here, running Firefox, mc, and xterm:

For a list of included packages, see: http://grml.org/files/grml64-full_2017.05/dpkg.list

For more info, check out the Grml website: http://grml.org/
Grml at DistroWatch: http://distrowatch.com/table.php?distribution=grml