Earlier quoted context omitted.
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 grow…
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'…
Anyway, thanks for the guide.