After running CCleaner with v.2.26.1050 with Firefox 3.5.6, it seems to clears the history but when you switch the Firefox History pane to View By Site, it still lists every site folder. Each folder is empty but they are all still there.
Just thought I'd mention it. I'm running Vista Home Premium SP2.
I think its because CCleaner will corrupt the places.sqlite file which stores the history. The only way not to have this happen is to first clear Firefox with its own internal history cleaner, then run CCleaner after you close Firefox. But if your places.sqlite file is already messed up you have to delete it first. Doing it this way kind of makes CCleaner useless though for cleaning Firefox but its the only way I know how to prevent CCleaner from messing up the places.sqlite file. I don't know if it's possible for CCleaner to ever clean Firefox correctly, but it's been this way since Firefox 3.5 came out.