Firefox actually purges history automatically. For instance, the oldest history I have on this browser right now is from January 2018. I found about this the hard way.
I noticed this behavior in Firefox too. So I started writing personal Python scripts to scrape FF's SQLite database where it stores all the browsing history information.
It looks like Firefox has been doing it since 2010[1]. I wonder how long Chrome has been doing it, since launch, 2008? Here's a Chrome bug discussing it[2].
I have this problem. Some bits of history are gone except from old backups of profile directories and profiles where I've already set places.history.expiration.max_pages to some absurdly high number.
I need to do a handful of experiments to see exactly how this interacts with Sync, even though I've (foolishly) already synced the important profiles. I'd hope that the cloud copies of the places database just keeps growing, but in any case, I'd rather combine them all offline anyway.
Even if you set the setting, how can you be sure that it won't be reset on an upgrade or that you'll remember to set it if you need a new profile (perhaps your old one becomes buggy, crufty, corrupt, or all three)? I thought I had all my history retained until one day I couldn't find a website I knew I had visited years ago, and took a closer look at my history and was very unpleasantly surprised... What happened? I'll never know, but my suspicion is that Firefox reset the history retention setting at some point along the way. If you do any web dev, you know Firefox occasionally backstabs you and changes on updates. The only way to be sure over a decade-plus is to regularly export to a safe text file where the Mozilla devs can't mess with it. I can't undo my history loss, but I do know I have lost little history since.
I can't be sure. When I say 'combine them all offline', I mean using something like [1] which refuses to do anything for me because the Waterfox database version is a rather old Firefox version, and that seems to expect all the db's versions to be up-to-date and equal, which seems pointless. #include <sqlite3.h> was my next step-- only I don't walk very well, so that didn't happen "yet". Or I'm lazy, or distracted, or depressed, or something. When I recently got tired of realizing a thing was on the other machine, I bit the bullet and synced them, if only to see how well that worked.
