I’ve noticed for the past couple days, there seems to be a constant read/write with my HDD when I open up Firefox. After trying to find out what it was, I decided to do a Google search for it, which brought me to a post on gHacks.
There is a fix for Linux where you set the Urlclassifier.updatecachemax from -1 to 104857600. When it’s set to -1 it means the cache is unlimited, now set to 104857600 it means it’s limited to 100 Megabytes.
To set it, open a new tab in Firefox and in the address bar type in about:config then in the search bar at the top, type in Urlclassifier.updatecachemax. When you see the result, double-click on it and change it from -1 to 104857600.
I hope this helps. I will monitor my HDD usage over the next couple days and see if it fixes it.
Update: Well, it seems setting the Urlclassifier.updatecachemax helps a little. I can still hear/see the HDD reading/writing from cache, but only lasts about 40-60 seconds, instead of a couple minutes.