Firefox writes megabytes of data per minute to disk, why?
There is a setting in Firefox that controls how often the session restore saves files. Go to about:config and change:
browser.sessionstore.interval to change how often the session is saved. On my system, the default was 15000 (milliseconds) so it was writing to disk every 15 seconds. If you increase this to 300000, it will only write every 5 minutes.
browser.sessionstore.enabled can be turned to
falseto disable this feature completely. This will reduce the amount of disk writes Firefox does, but this will also prevent Firefox from restoring your session when it crashes.
I did an investigation of where writes to my SSD come from. I found the same thing you did. After analyzing logs of writes as well as thinking about things I realized that it is Firefox's crash recovery. In order to be able to recover from a crash Firefox has to write the session to disk. The session information is stored in the four files you listed. Firefox updates these every ~30 seconds. With lots of tabs in a big session this adds up to a few GB per day.
But as surfasb says, it is not really anything to worry about.
After loading about 10 pages and some in Chrome mine looks like this:
So I guess that's normal swap/page file use.
(Although one would think with me only using 31% of RAM it wouldn't swap at all.)