By default Firefox puts its cache in the home partition.We can speed up Firefox and reduce disk writes by moving this cache into RAM if we have 2GB RAM or more.
1. Edit /etc/fstab,open terminal (Ctrl+alt+t or) from Applications->Accessories menu and type:
sudo gedit /etc/fstab
Add following into this file and close it:
tmpfs /tmp tmpfs noexec,defaults,noatime 0 0 tmpfs /var/tmp tmpfs noexec,defaults,noatime 0 0
2. Edit /etc/sysctl.conf:
sudo gedit /etc/sysctl.conf
add this line and save it:
vm.swappiness=1
3. Type about:config in firefox address bar and click(I'll be careful,I promise!.) Right click on blank area and create a new string value called browser.cache.disk.parent_directory, set its value to /tmp
Now, reboot the system and experience the performance.
Sandeep Bhalla's Blog 