Make a copy of your profile (to preserve your history) then in Firefox's Show All History window, search for a site that has thousands of visits, select them all, then press delete. Firefox will start burning a few CPU cores and lock up for a long time, every time.
That might very well be performing poorly. But I interpreted the OP to talk about usability of viewing all the previous history. My goal is to never delete my firefox "sites visited" history so I can refer to it back later. So naturally I've never experienced the problem you're describing.
My places.sqlite is 400MB, and just opening the history viewer is enough to cause Firefox to hang for several seconds. It's really not designed to store history forever; I even had to change places.history.expiration.max_pages and places.history.expiration.transient_current_max_pages in about:config to prevent it from deleting old entries.
