brent Each to his own, choice is a privilege that should be consumed to the full.
A brief guide for running Firefox cache in RAM taken from my own notes.
about:config
MOVE FIREFOX NETWORK CACHE INTO RAM - Needs 2 GB OF RAM OR MORE
browser.cache.disk.enable
set to false.
browser.cache.memory.enable
set to true.
browser.cache.memory.capacity
Change from -1 to 524288 (KB, = 512 MB RAM)
That's it. I keep my cache fairly low and most stuff seems to work fine. The setup is especially good for old slow machines but you can give yourself more cache if you have lots of RAM.
I am quite sure that googling the about:config entries will get you far more information than I supplied here.
Happy tweaking.
Edit: Got rid of silly size letters in first draught.