If you are using FireFox or IceWeasel AND you are a miser like
myself using only 2 Gb for your LiveUSB, you may want to review
your browser's default 'Off-line Cache' limit settings.

In making a recent occasional personal backup, which initially
took 60Mb, I was surprised to find it took 160Mb. No structural
changes had been made that would account for that sort of change.
Since .mozilla always takes the most space in my backups, that
was immediately suspect. Sure enough, the biggest change was a
result of a change in the size of .mozilla's 'Offline Cache'.

When I investigated IceWeasel's Edit>Preferences>Advanced GUI
panel, I found that the Offline Cache default setting was
automatic and likely set to 'no more than 1024Mb'. I have
decided that is MUCH too generous, and have reset my
preferences to 'override automatic' and 'limit cache to 60 Mb'.

I'm wondering if, for back-up purposes, it might be just as well
to omit this off-line cache from the back-up altogether.