In order to minimize writing to disk you could try to move your firefox cache folder into /tmp we created earliner in our RAM.
In your “about:config” add the following entry:
add a string value of “/tmp”.
Ofcourse your cache will be erased each time you reboot, but who cares we are trying to minimize disk usage, so that we can prolong our battery life.
Since I have created 100MB /tmp drive, I have decided to leave firefox cache at the default setting of 50000 (50MB).
browser.cache.disk.capacity (integer) 50000