Is there a reason you are using an old version? https://support.mozilla.org/en-US/kb/update-firefox-latest-version 49

What type of document, and how long ago was it accessed? And when was it removed?

It would be better to download a file you want to keep.

hmm, I'm using 37.0.2 Probably because there was something else it did that didn't work for me, most likely mess with the usability of the "plain old favorites" add-on when updating. that is the most frequent reason I would go through the trouble of down-dating Which is the latest version that supports plain old favorites? ( I can not use bookmarks, no matter how much you tell me how nice it is)

Anyway, this is something new that has started happening all by itself without me up-or downdating. This is the web site I'm talking about: http://mcle1.co.mendocino.ca.us/NewWorld.Aegis.WebPortal/Corrections/InmateInquiry.aspx

You enter from and to dates, and get to a list of inmates. then click on an individual, which comes up, then you look at it that person for a moment, and TRY to go back to the list of inmates, which is where the message comes. and if you look at 20 people, you have to "try again" 20 times which out here in the country where even high speed internet is slow, takes 1-2minutes to reload. But - isn't there a way for me to control when it keeps things in the cache? Everything I find on the internet is about purging the cache.

I see. This is a common problem. What I do is; Right-click a link you want to check out and select Open New Window/Tab. Once you are done, close it and you are back where you started from.