there's a pref to set max days of history to save, i think. or at least when to mark it safe to delete.
hm, i thought there was
well, it was browser.history_expire_sites and it might have been removed
ah yeah, here's where it was removed: https://bugzilla.mozilla.org/attachment.cgi?id=417484&action=diff
i think it was part of a cleanup to make async places expiration work for multiprocess firefox
XndrK: this may work: https://addons.mozilla.org/en-US/firefox/addon/expire-history-by-days/?src=search
one review says it doesn't, but others say it does