CCleaner v. 2.26.1050; Firefox 3.6Bet4; Windows Home Premium: Select Applications:/Firefox/Mozilla, Compact Databases.
CCleaner hangs on the Brief.sqlite database in the FF profile.
Brief extension: https://addons.mozilla.org/en-US/firefox/addon/4578 . Yes, I know it is supposedly incompatible with FF 3.6, but it can easily be made to work (with a few things that need to be fixed for 3.6, but those things don't affect the sqlite database as far as I know.)