Not a good answer ... sessionstore retention has nothing to do with browsing history.
Well, there you have it. Note the name "cluelessuser" is appropriate!
My observations on my system are not generalizable...
OK I shutdown firefox and checked for and found sessionstore.js, however, when I restarted firefox the sessionstore.js file is gone. So that might account for why I couldn't find it whilst firefox was running. So it would appear that the sessionstore.js file is written on closure, which seems strange to me as in the instance of a crash or abnormal shutdown how would this file be written.
Nor do I understand why there would be sessionstore-n.js files if only one is supposed to be stored, I would have thought it would overwrite the sessionstore.js file
On my system, while FF is open, there is always at least sessionstore.js and sessionstore1.js. I always assumed that the sessionstore.js holds general parameters of the session while sessionstore1.js tracks tabbing and browsing history to update sessionstore.js.
There have been times when I've had up to sessionstore3.js. Perhaps if sessionstore1.js is (for whatever reason) still in existence, it will create sessionstore2.js, etc.
My system is old and slow, so it will sometimes take up to a minute for sessionstore.js to 'go away' after closing FF (also, I have other system complexities that may contribute to that timing).
BTW, I see this exchange going on continuously while running Avast Standard shield, as it is scanning both sessionstore files while I 'surf'... which is one feature of Avast that I like!
I 'know' it is working for me...