problem on application.tmp_dir under linux

there is a way to change the temp directory /tmp to home of the current 
user?
if i change "application.tmp_dir" in unix.js to point at "~/" (the 
default is "/tmp") i have no result.
why there isn't a way to handle stream (like mp3 or ather media files)
without download them in /tmp first?

in the old netscape comunicator i don't have none of this problem.

excuse me for my english, but my native language is italian:-)

bye bye