A few days (or a couple of weeks perhaps) ago there were similar posts about Chrome and Firefox, but in the browsers it was related to writing the metadata to reopen every tab and sesion back when you restarted the browser.

Firefox comes pre-configured with a time of 15 seconds intervals, that is, every 15 seconds it writes a few KBs of data just to reopen your session, no matter what' activity you're doing with the browser (or if doing nothing at all). At the end of the day it ammounts to a few GB's in writes, depending on your browsers usage.

So it's not crazy/paranoid/weird to asume that this is becoming more or less "standard" behaviour.