The restore interval write function of Firefox (and also Chrome) produces a lot of writings over the day, according to servethehome.com.

Solution

Go to about:config and search for browser.sessionstore.interval (given in millseconds)

This is by default set to 15 seconds and causes the high integrated written bits over a day - more 10th Gibibytes (GiB) per day..

I’ve set it to 30 minutes, so in my configuration

browser.sessionstore.interval = 1800000

Restart the browser and that’s it.