I finally got a wifi card working on my zaurus and started playing with firefox
straight away when i came to download something i ran out of space .
its basically because it tries to write files to /tmp !
the way to change that setting is to..
in the uri bar type about:config this will bring up the firefox tunables.
in the filter bar bellow type applications.tmp_dir or tmp_dir
it should bring up the setting as follows
application.tmp_dir type string value /tmp
double tap this line and change it to say /hdd3 or where ever you have space (flash drive sdcard).
and away you go , it'll now store all tmp files there before completing the download to the correct directory .