The way I reduce disk i/o is by editing my /etc/fstab file and adding ‘noatime’ flag to my drives, then adding this to the end:
tmpfs /tmp tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/log tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/tmp tmpfs defaults,noatime,mode=1777 0 0
tmpfs /var/log/apt tmpfs defaults,noatime,mode=1777 0 0
Also by editing my /etc/sysctl.conf file and adding this line:
vm.swappiness=15
And as for the browsers, most chromium based browsers have a lot of disk access for cache, but in Firefox I disable the cache by going into about:config and changing these:
browser.cache.disk.enable (false)
browser.cache.memory.enable (false)
browser.cache.offline.enable (false)
network.prefetch-next (false)
browser.sessionhistory.max_total_viewers (0)
browser.sessionstore.interval (600000)
Remember to reboot for changes to take effect.