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.)
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 has a built-in sqlite vacuuming function: when you right-click on its Trash and choose "Empty Trash" it will ask if you want to compact the database. If you haven't done so for a long time it can take a few minutes. You might try using this function and seeing how long it takes, to compare with CCleaner's performance at the same task.
I should add: on my system (WinXP, FF 3.5.5), CCleaner does pause for a minute or so on the brief.sqlite database, but it also take Brief about the same amount of time to do its work.