Ramdisk

Linux
By default Linux 1/2 of your RAM as a ramdisk. You can put the files in /dev/shm.

Ubuntu 9.04
vi /etc/fstab

and add a line at the bottom:

none /tmp tmpfs size=256M,nr_inodes=200k,mode=01777 0 0

This will take 256M of your RAM to use as /tmp in a ramdisk situation. You can adjust the 256M to say 1G, depending on how much RAM you have available. Reboot for the settings to take effect.

Firefox
vi /etc/fstab

and add a line at the bottom:

tmpfs /media/ramdisk tmpfs size=100M,nr_inodes=10k,mode=777 0 0

This allocates 100M of your RAM to use a a firefox cache. In firefox type

about:config

in the URL bar, and add the following setting:

browser.cache.disk.parent_directory

and set the value to

/media/ramdisk

as in your fstab entry above. Reboot for settings to take effect.