Might be OS dependant? My Firefox does not reload the page, it's just "there". I have to refresh to get an update of the page (I use it for forums).

I'm on Windows if that makes any difference.

I think it rather depends on the page (some pages with lots of dynamically generated content might mark themselves as no-cache/no-store), and in any case if you don't use a tab long enough, sooner or later it'll be evicted from the browser cache.

Maybe, just running on bog standard Linux Mint. Nothing fancy.