Firefox Portable (3RC1) $TEMP writing

Generally, during use firefox tries to write to the host machine's $TEMP folder. I would like to disable this, to avoid any risk of an undelete spying. Most data that ends in $TEMP is temporal files, whose contents I don't know. But I don't want anyone to see I watch videogame speedrun videos (some people using those computers would not like that, think of Jack Thompson-y mentality, and also general privacy).
I have used a firewall/watchdog app to monitor all writes to the host disk, and generally most data written to it can be stopped without Firefox complaining or failing, but starting a download, for some reason, unless it's done by "save link as...", does, as well as installing extensions, forcing me to disable the security app to allow writes. (the default download folder is set to my portable drive, so it "should" not write anything into the host) (Note: some redirects won't play fair with save link as..., I use downthemall for those, but with special download sites such as rapidshare I don't like the idea of the download failing and forcing me to wait as if I did download something).
Is it possible to force firefox to use its root drive (say G or H or so) to store such data without touching the host hard drives, thus leaving them untouched?